Dear ajmiami: If you have been taking your birth control pills correctly, pregnancy would not be the most likely explanation for your cycle changes. Nonetheless you might want to do a home pregnancy test just for your own peace of mind--and that of your friends.
If the test results are negative (which I would hope and expect) there are some other explanations. The most common would be breakthrough bleeding due to the hormones in your pills. Alas, breakthrough bleeding (BTB) can be a common side effect of most types of hormonal birth control (eg pills/patch/ring/shot/Mirena IUD). Among birth control pill users BTB frequently occurs after a missed or late pill. In your case it sounds like you are careful to take pills at the same time daily. More remotely, BTB in a pill user can arise if she has gotten a chlamydia infection. Yet, if you both are monogamous this is not going to apply.
When a woman uses hormonal birth control it can make the lining of the uterus more unstable--so it is easier to have some of it begin to shed. Sometimes the lining is less stable because the hormones make the lining much thinner (actually this is good as a thin lining is a healthy lining). Sometimes the lining is unstable because the hormones can make parts of the lining out of synch.
In terms of the increase in cramping,and heavier flow, that can arise if there is a pelvic infection (eg chlamydia or gonorrhea). As your friend correctly stated, fibroids of the uterus can prompt heavier bleeding and in some cases more cramping. Yet if you are in your 20's symptomatic fibroids are much less common than in one's 30's or later.
Bottom line, BTB on hormonal methods of birth control is a nuisance side effect. The protection from pregnancy should still be in effect. You should return to your GYN or clinic even before your annual exam if the increase in pain persists. They can also readily evaluate you for infections, or fibroids. Often a change in the brand, or formula, of birth control pill will fix problems related to the hormones in your brand of Pill.
Yours,
Jane