Brown discharge for more than a week. 3+ weeks after intercourse

I had sex about a month ago (May 29 for the first time) I didn't experience any pregnancy symptoms like sore breasts, nausea, etc. Problem is I have an irregular period. 23 days after sex (June 21) I thought I finally got my period. However, later in the day when I checked my pad, there wasn't any blood, just a sort of brown discharge. It was dark (but not black) and it wasn't as wet as a normal discharge. I took a HPT and got a negative (June 26) I figured that a 4 week wait was long enough, due to the fact I can't really wait for a missed period - since mine are off. the discharge can't be implantation because I've read that should only last about 1-2 days. This discharge has been going on for a week and 6 days. However, in between these days, it turned to a lighter brown. Sometimes I wouldn't see anything on my panty liner, only when I'd wipe. (July 2) I don't think I even had the discharge. Last night (around 12 or 1am) I got the discharge again. It came out really wet, and a brown color (not too dark or too light) When I checked this morning it dried to a really dark brown, dry discharge. (it wasn't wet but it's sort of sticky in between my fingers) What might this be? I've searched online and people link it to things that aren't too serious, like stress, and then to more serious things, like pregnancy or infections. I have not experienced burning sensations or painful urination. Could this be due to my irregular period and not have anything to do with the sex 3-4 weeks prior?