Pregnant or late time of the month?

Me and my boyfriend had un-protected sex once not even about a week after my last menstration. I knew this wasn't right, and a few times after that he had himself inserted into me. But not for long. It can barly be called sex. I hasd my last menstration on March 24th, and now it is April 30th. And I skipped all of april without one. And now its coming May tommorow, and I dont have any of the signs of a coming menstration that I get most of the time (Cramps, Lower back pain). I took a First Response Pregnancy test on sunday the 27th of april, one thats suppose to detect the pregnancy hormone a week before your expected menstration, and it came up negitive. Im saving the next pregnancy test to take this sunday, if it doesn't happen by then. I have been stressed out, and losing sleep in the month of April. That could be the reason for the late menstration, but that has never been a reason for me before. I also think my stomach is getting alittle bigger each time, and solid. Not as squishy. It looks like my stomach is pushed out a bit, before I even push it out.
I know I could be pregnant, But what should I do?
What are my chances ?

first off im not what people call 'experienced' but I would say to talk to your mom & your doctor abut it. also make sure that you are not stressing so much.

hope my advice made a difference ^_^

Ok, well all I am going to tell you that anytime you have sex, there is always a possibility of pregnancy, and ALSO! especially if it is unprotected sex, I am not your DR. so I cannot tell you, but I will advise you to take a pregnancy test, and then if you still have suspicions, seek your family dr. good luck. :]

It doesn't matter how long he had it inserted in you - that really makes no difference. Obviously there is a high chance that you are pregnant and a chance that you caught and STD- but there are other things that could cause a late period; stress, body changes, etc. You mentioned you are under stress so it could have something to do with it. You need to go to the doctor and get a blood test done - they are more accurate and detect pregnancy sooner in your cycle.