Need Opinions!! Possible Miscarriage!!!!?

Alright, I am 5 weeks and 1 day today, so I am not very far along, but the doctor has been monitoring my HCG levels since last Thursday due to bleeding. My numbers have risen greatly, and she is very pleased with the rate that they are rising. The bleeding that occured last week completely stopped until last night. For about 20 minutes, I had a reddish-brownish bleeding. It wasn't too heavy, not enough to soak even a panty liner, and it only happened when I wiped. I called the doctor to report the incident, and she said that as long as I am not cramping that there is no need to worry yet. I go in tomorrow for another blood test, and then next week after I reach the 6 week mark, we will do an ultrasound to make sure we can see the babys heartbeat. What I am wondering is if any ladies on here have experienced slight bleeding in the first trimester and went on to have a healthy, happy baby. And also, do you think that sex can cause the bleeding that occured? My husband and I had sex Saturday night, and immediately after, I had brown discharge, and then Sunday night we had sex, and Monday afternoon I started bleeding again. Is there any correlation between sex and bleeding during pregnancy? Thank you ladies!!