Suggestions on what might be wrong?

So I been having unpretected sex with my boyfriend hoping we can have a baby I usually have my period around the 16th well this month I had it around the 8th and last about 4 days like normal but then yesterday I started bleeding it's not bad it's almost like spotting. I haven't been stressing at all, and haven't really changed my routine. I also have gained 6 pounds in the passes week I can't stop eating any suggestions on what's Goin on?