im so scared right now

I had an IUI October 31st, and it has been 16 days. Yesterday after having sex with my husband, I started to bleed very lightly. You could barely even tell. And then I put a tampon in thinking maybe I was starting my period since yesterday was the day. 8 hours later I removed it and it was like a brown/red color. And not even full. I thought for sure it would be the implantation bleeding. But then this morning, I started bleeding heavier and it went to red blood. But Im not sure if its continuous or not becuase of the tampon. For the past 2 weeks I have been having crazy pregnancy symptoms and thought for sure I was pg. My husband is a Identical Twin and our chances for mulitples is very high. Could my bleeding be that from multiple eggs implanting into my uterus? I took a HPT and it said negative. But I have this intuition I am PG. Anyone know what it could be? Im calling the doctor tomorrow since I need to go in for Clomid again. But i dont want to take the clomid until Im sure im not PG.