My period lasted for 2 days then it was gone. Could I be pregnant

can anyone help me out. for almost a year my cycle has been 25 days and my period always last 4 days. for two months, my cycle changed and was 27 days, and my period was lasting for 6 days. this month my period came on sept 18th. Which would mean my cycle was 23 days. On the 18th, I got my period, it started light then an hour or two later it was heavy. The next day, (19th) it was light again and was gone by the night. The next day, (20th) I had s_x with my bf. And it came back but only when I wipe and it was dark in color almost looking brown. I spoke to my doctor over the phone and he said he wasn't sure because implantation bleeding isn't that noticeable. Since it was heavy it could mean that it was just one of those months when your period acts weird. He said just to be sure take a pregnancy test in a week. I have been getting heartburn in the morning, cramps and I was going to the bathroom every two hours. I figured I was probably drinking to much water.  My question is, Did anyone get a heavy implantation bleeding? And could I be pregnant? or am I just getting my hopes up?