What Causes Irregular Periods After An Abortion And Chances Of Pregnancy?

I had an abortion on 12/7/13......everything went well but I bled until 12/28/13 that s when my bleeding stopped..................I started spotting on 1/30/14........and I say spotting because it was not like a regular period, (I am typically ALWAYS regular.....i.e.....5 days on, 28 days off). It stopped a week later. It has not been back on since. I am 36, 200lbs, 5 6. I have had 1 child by C-section in 2006. I had sex 3/15/14 with X.............I had sex 3/29/14 & 4/5/14 with Y........ How can I determine who is the father.........if I am in fact pregnant. .................???????????????????????