Spotting and cycle questions.... help!

So my typical cycles for the past 3 years have been around 29 to 32 days in length. The husband and I have been TTC for a little over 2 years now. I have always had weight issues and been overweight. After a recent check out by my OBGYN it was determined that if I could lose some weight it would increase my chances of concieving. So almost 8 weeks ago I embarked on a new fitness and nutrition program. I have since then dropped 15lbs. My last cycle which started August 3rd came 2 days early (27 day cycle) only lasted 3 days ( typical for me is 4) and was very light in comparison to normal. Never more than a half dollar amount in a day. I took a pregnancy test the day before the bleeding started BFN. I took another test a week after bleeding BFN. Then on the 11th of August I had spotting that lasted maybe 3 or 4 hours at most. Only noticed when wiping and very light pink. I didn't mark when the BD'ing happened because I got tired of keeping track at this point. Not sure what to think or if I should be concerned. Any thoughts? TIA