TERRIFIED of 2nd miscarriage!! Please help!!?

I miscarried my first pregnancy this ped March at 6 weeks pregnant. I just had a BFP a few days ago, probably about 4 weeks pregnant, and I am terrified I will lose this baby as well! I also have a condition called Interstitial Cystitis, which I am not sure will affect my pregnancy, or if it caused my previous m/c. Doctors say No. I am so scared!! How can I be happy about this baby, when I am so terrified I will lose him/her? Any advice??