First date of second to last period : Jan. 24th
Last period : Feb. 16th
Now I'm starting to spot again.. march 5th
The bleeding is more of a brownish color and only when I wipe do I see it.

Ive also had unprotected sex during what should have been my ovulation days after the feb. 16th cycle. So what could this be also I have had a headache since yesterday.

That could be a little mid cycle spotting. It can happen. Though there is a good chance you could be pregnant, I don't think that is the cause of the spotting. You are going to want to take a pregnancy test to know if you're pregnant, but you'll need to wait until about two weeks after your period should have started.