Me [25F] with my sister [29F]. Sister told everyone I was on hard drugs when I was actually really sick

I don't even know where to start.
For years, I was having these weird health problems; I couldn't sleep, was anemic, had horrible pains in my lower abdomen, and could barely eat because of the pain. I saw many doctors, and none knew what was going on with me. I was told it might all be due to a gluten-intolerance or lactose-intolerance, and to change my diet (which I then did but it still didn't fix my issues).
Due to my health going to ****, I started spending more time at home, and was forced to miss many family events. When my family did see me, I looked like ass; super skinny, big black circles under my eyes, and just generally looked like ****. I also changed my diet around. They thought how could I be gluten-intolerant when I ate gluten my whole life with no problems. My family thought I was just being difficult.
At one point a few years ago, I was with my sister heading to my mom's birthday in her car. She asked me what was going on with me, and I said I wasn't feeling well and was having some health problems. She said straight up she didn't believe me, and implied it was because I was on hard drugs. I do smoke weed, but do no other drugs. My sister is religious, so I just assumed she was paranoid. We were about to go to my mom's birthday, so I just let it go.
A little while after the birthday party (months), I had to call my sister about something. I can't remember the context, but I think it had something to do with me bailing on another family event. I over heard her husband say in the background in front of their kids " she'd come over if we had drugs". I was like " what did he say?", and she was like, " Oh he was just joking..." Even if he was joking, this type of joke ****** me right off, because it was in front of their kids.
My sister eventually stopped letting me see her kids. Anytime I asked if I could babysit them, she'd make up an excuse to not have them over. One time we had arranged for me and my boyfriend to take her 8 year old daughter and 5 year old son for a day of painting canvases, and she called me up the night before saying her husband had to do an oil change the next day and had no time (really? of all excuses she uses something that takes under 15 mins). I was ****** because I just went out the day before to buy a bunch of painting supplies for the kids. This incident became one of many.
Fast forward to 2019; I recently found out that these health problems were due to a benign tumour the size of a grapefruit that was lodged in my uterus, but was pushing on my intestines, bladder and other organs. I am due for surgery in a few months. Once I found this out, I told my mom, who then told my sister. My sister texts me, interrogating me like she can't believe I actually have real health problems, and if it was really that big why is my surgery months away and not weeks or days? I had enough of her **** and called her out on it. I said " I'm getting the vibe you don't believe me" then I sent her a pic of the paper work showing the mass inside me was 11x10 cms. Then she goes " Oh, so you really are sick". Then I said " are you sure you believe me, and you don't think I'm on hard drugs?" Then I reminded her of our conversation in the car before my mom's birthday. She completely denies that conversation ever took place. She said she couldn't remember saying that, and if she did she was just joking. I was like, how is saying I'm on hard drugs a joke (btw, nothing about her tone in the car implied it was a joke. She was dead serious).
The damage didn't just stop at her family, she convinced my parents I was even on hard drugs. And they still don't believe me! They're literally waiting for me to have the surgery in order to be convinced I'm actually sick.
I do have mild aspergers, but I feel as though she's taking advantage of this and is gaslighting me. My boyfriend even agrees she's gaslighting (he's my voice of reason in times when I really don't know).
I'm sick and tired of my family's bull****. I was at my worst, and all she did was kick me while I was down. The fact she can't even own what she did makes me want to cut her off (how can we fix our relationship when she can't own her actions?). She manipulated my parents, who then told my aunts and uncles even. The whole damn family thinks I'm on hard drugs. I have no relationship with her kids, because she keeps them away from me. The only time I'm allowed to see her kids, is at family events with the entire family, which happens on a yearly basis.
Is this a valid reason to cut her off? Am I over-reacting? I feel like cutting my parents off too because they still don't believe me. What's the point of having a family if they don't support you, and just accuse you of things you aren't even doing? I'm the only one in my family that isn't religious, and because of it they are teaming up against me.
tldr: Family thinks I'm on hard drugs because my sister told them I was when I was sick. My relationship with my family is so damaged now, I'm tempted to cut them all off.


Source.