BFP, followed by BFN, then AF shows up😢

Maya • Mama to a perfect little boy 💙 Expecting boy#2 in August!!
Sorry it's so long, i just need to vent😔.. So as the title says, I got my BFP on 15dpo, one day late. I was over the moon excited.. I have PCOS, and we've been TTC for 2 years now, and this would've been my first pregnancy, no other losses.. I tested again, 16dpo, line was still there..but it was  a little lighter than previous day, and I just knew something wasn't right:/.. I was feeling super gasy, constipated, crampy, and my face, hands, and feet felt swollen, up until then.. So I waited 2 days to test again to make sure hcg got the chance to double, but in my gut I knew it wasn't right, and my symptoms started to subside, and the cramps felt different.. So I tested at 18dpo, and I got a BFN.. AF started that day, which was yesterday.. Now I'm bleeding more than usual, and I'm passing more clots than I normally do.. I just assumed it was a chemical.. I have a doctors appointment today to see what happened.. 
Idk if it happened because I have PCOS, or is it just that common.. How many of you ladies had a chemical? How did you deal with it? How long did you wait to start trying again? 
Thank you for taking the time to read this, and respond! I'm so glad I found glow, you ladies are such an amazing group of women!! I appreciate all of the support❤️!!!