Struggling

We've been TTC for over six months (which i know others have struggled longer), I have health issues and honestly don't know if I can get pregnant and carry to term. I've miscarried once three years ago. But I just found out my younger sister is pregnant and I'm happy for her of course but also devastated because she wasn't trying. I've been tracking my cycle, ovulation tests, temps, all of it. No luck. My husband has one child with his ex, so I feel like it's my issue. I'm currently five days late and have taken at least ten tests but they're all negative. I'm just feeling so discouraged and heartbroken.