I've read sooo many post online about women bleeding throughout pregnancy and Dr's do not know why! How could this be?!

Let me add I'm 15 weeks 2days and I have been bleeding for 2 weeks now. Some days more and some days less. Some days Brown and some days deep red. I've had 1 u/s and 2 swabs/exams everything was fine. I've had multiple dopplers done and baby's hb is still strong. I've been on pelvic rest and now off work and I'm still bleeding.....Now every little cramp scares me. Just wish Dr's could figure it out alrdy.

Also I've experienced 2 chemical pregnancies and 1 Mc at 7 weeks. Please God let me have this baby!