Slim chance but not sure!

I was on birth control pills for about 10 years for my endometriosis and in June my husband
and I decided to try for a baby. My periods have been fairly regular since getting off of the
pill (about 25 day cycle), until this month. It was very heavy for one day and then only lasted
for 2 more days (done on Monday morning). The only possibility for conception would have been
Thursday of the same week. That seemed too soon for me (unless I had a 20-day cycle). About
5 days following the potential "conception day," I started bleeding again. Could be my endometriosis
or - could it have been implantation bleeding? How much bleeding would there be if it was implantation?
It started heavy, but then went away and I only had a small amount of brownish discharge. Then it
started again the next day, heavy at first and then disappeared. This bleeding lasted about 3 days.
The only other symptom I have is sore nipples. It's too soon to take a test so I was hoping I could get
someone's opinion. Thanks!

Kris