Brown Discharge (urgent.)

Okay, well obviously I have some brown dishcharge, not too strong... and it doesn't smell. I had previously been on depo birth control for a year and had been off of depo for a year without my period, so all together I hadn't had a period for two years. Well, last month I had my first period.. and it is now I think around two or three weeks since I had stopped. I had sex once during this time, (after I got off depo and before I started my last period) and did not use a condom. The discharge is a lighter brown.. so I don't know if it is spotting or just bacterial discharge. I have no pains, and it isn't heavy, just when I wipe and some gets on my panties. I've been through this before and I can never seem to learn, so I'm just afraid that my chances have run out. I think it just may be period related. Any help would be awesome.