What Causes Periods Which Are Excessive, Irregular With Spotting After Intercourse?

Hello Doctor,
I am 29 yesrs old, i am married befor 2 months, This monthe I got my periods 3 times in a month but it was only for one-one day and the blodding was very like like few drops, I did the pregency test after 37 days and it is nagative, but still I am getting periods for 2-3 drops
before marriege my perods was very regular, it is 30 days
I am really worried, Please help

Regards,
Shraddha