I lost my dad... 💔

My dad passed away 3 months ago & I hate how grief just sneaks up whenever it most desires. I was 25 when her passed, just turned 26, and ever since he passed I've had to step up and help my mom stay on track with the bills and I also had to become like a parent to my 14 year old sister. I've been grieving and trying to cope with being diagnosed with an infertility disorder for the last 8 years so helping parent a teenager before getting the chance to become a mom to a baby really but a downer on everything. Anyways, my sister relies on me for absolutely everything because our mom has a hard time saying no to pretty much everything, but parenting her is hard because even though sometimes I say yes & sometimes I say no... when I say no she still throws a tantrum about it and one time she even yelled at me telling me that I'm not her parent and will never be her parent. Like, why treat me like your only parent them? I rarely get to do things that I like to do, besides my job, because if I'm not helping with or driving them around then I'm home alone and have to care for our dogs. I'm really just venting here but any kind words or advice would be appreciated.