Spotting Before Cycle. Any ideas?

Hello. I had sex 7 days ago (and used a condom). I think precum could've been in the area but not much. It was the first time in 3 years and it was on an ovulation day according to the app. 
Now, I've been spotting for 4 days. It was bright red but now is more of a brownish red. My cycle is due in 7 days. I never have irregular cycles.  Any ideas on why the spotting is happening? Is it because I hadn't had sex in a while?