TTC & not sure...

Sheena
Hello! So I'm semi new to this app but I thought it might be helpful! 
My husband and I are trying to conceive and I finally started ovulating regularly last month. I got off the pill 3 months ago. Well my period is typically pretty regular and should have been here by now, maybe two-three days late... It's normally a medium flow as well. First day with a liner, then tampons after. We did have sex a lot in the beginning of the week of the 29th while I was ovulating...
Well 4 days ago I started having some spotting. It's more of a brownish color. I've worn a liner each day and the liner isn't full by any means. I have taken 2 tests (3 days again and yesterday) and they are BFN :( light cramps, nothing crazy (almost like a period, but less intense). Also, my nipples are sensitive... Not horrible, but certain fabrics bother me.
Any suggestions/thoughts on what this might be?