It's certainly not impossible to fall pregnant while on the pill, and if you take it irregularly, or have any kind of gastro problems, it makes it more likely. However cramping probably isn't the most common symptom in early pregnancy, and if that's the only thing that's different, I wouldn't immediately think of pregnancy. On the other hand, it's obviously making you quite stressed, and I always think it's better to know than to worry!

If it were me I would do a pregnancy test without telling my DP, but that's just because he wouldn't have much he could do to help me feel better, he'd jsut tell me to go get a test! I would do the test, and then definitely tell him if it were positive, and maybe tell him even if it were negative.

If you test, and the test is negative, consider going to see your GP anyway, because there are lots of other possible causes for lower abdominal pain, such as thrush, UTI, etc, and severe cramps that are not part of your usual cycle should be investigated.