Does Metformin counter the helpfulness of birth control? Does it make periods heavy?

I don't know that this is the answer, but I have a guess. Young women with insulin resistance are likely to also have a co-morbid condition called PCOS (poly-cystic ovarian syndrome). High insulin levels (that you WOULD have had), and PCOS, would cause your ovaries to push out more androgen hormones, such as testosterone. The result of this would be acne, more body hair than usual, and fewer or irregular periods.

What may be happening to your body is that the Metformin is regulating the amount of glucose in your blood, reversing the insulin resistance (i.e. making your body more sensitive to the insulin that your pancreas IS pushing out), and lowering your risk for diabetes. Your reproductive system may be starting to function more normally. I know many Many MANY women who have PCOS and have taken Metformin to initiate regular menstrual cycles, to be able to finally conceive. This is clearly not your intention, but your symptoms indicate that the metformin is working exactly as it should be. And so this also means that you may need to be more careful with your birth control than you were before. You may be more fertile, is what I'm saying. If you take an oral contraceptive, and you were lackadaisical about the time of day you took it, or accidentally missed a day here or there and nothing happened, you need to probably set up an alarm on your cell phone now so you are sure to not forget.

If you have a dissatisfaction with your weight, you are in prime territory to lose weight if you introduce healthy nutrition and some exercise - if you tried before and were frustrated by a lack of results, my suggestion is that you try now, as your results may be very different.

Metformin CAN lower your body's ability to absorb B vitamins and folate, so it's a good idea to take a multivitamin (specifically with B vitamins). Be careful drinking alcohol, as you're more likely to develop liver problems. If you're a regular drinker (multiple drinks each time you go out), your doctor may want to switch you to other treatment options - or you could decrease your use of alcohol.

As to your concerns about metformin making your oral contraceptives less effective... there are medical professionals who specifically prescribe oral contraceptives with Metformin for their anti-androgenic effects, and to help counteract an increase in insulin resistance (which comes from the oral contraceptives!) Oral contraceptives are never perfect, nor are people and their schedule in taking them; however, what will increase your fertility is not Metformin changing the efficacy of the contraceptive, but your body's reproductive system becoming more a more healthy environment to carry a child to term. This may not have been possible before with your insulin resistance (and possible PCOS).