I believe it is highly unlikely that you are pregnant. However it would be best to put your mind at ease. You can find inexpensive pregnancy tests that are very accurate. I wish you all the best in you new relationship.
Since you are on birth control, I wouldn't say the likelihood is high. The symptoms you are having could be related to your period or a number of other things. Since you are questioning it, I'd just get a test to put your mind at ease either way, but I would guess the test would be negative.