Light Periods. Going to get the periods?

First day of period was last month 11th Feb. Intercourse on CD14, CD16 and CD18. From CD20 I had an erected nipples, and cramping on and off on both the sides Performed the home pregnancy test its negative. Also visited the already scheduled general doctor visit on CD 27 she suggest but both urine and blood test are negative. Later Period is delayed by 2 days, pregnancy test is still BFN This morning period came was happy that finally things started to clear out. But it came only for few hours, as brown in color not blood red as it used to be. I have a very regular period of 28 days of 2 to 2.5 days of bleeding. This is the first time ever we tried to conceive. What is the possible cause? Can it be the implantation bleeding? Why it stopped ? Am i still going to get the periods?