One of my niece's friends got pregnant at 13. And one of my friend's growing up was raped by her brother until she was 11/12. It happens so I never doubt the possibility.
You can also gain weight because of the birth control (typically is more common with the depo shot). And excess weight can halt a period too (typically you need to be pretty obese for this though). Although like I said sometimes, it's just a little off until you get older. I wouldn't worry too much about it.
Although you may want to talk to your mom about being on the pill. I mean if you're not sexually active/have no immediate intention to become sexually active and your periods are usually not bad- then why be on them? It's a good idea to know why you're taking medication and you're at the age now where you need to start taking over your own medical health instead of relying solely on your parents.
Who would have sex and 14? o_O I can't remember why I have them, I think it was because my sister got really bad cramps and stuff and my mum wanted to get me some in case mine were bad to but they weren't.
I have gained a bit of weight but I think thats just because I'm a fatty :L, and i'm not stressed.
Birth control pills stop your monthly cycle so you wont have a bleed if you take them constantly however, you may bleed a little on your week off if you have one. I personally wouldn't worry about it. I started my periods when I was 12 and they didn't become regular until I was 16. Please note that even although you are on the pill, you can still get pregnant when you don't have a bleed so if you are sexually active then please take care.
Are you sexually active? Why are you taking birth control? Hormonal changes can cause periods to stop so your birth control might actually be causing it. Also weight gain, malnutrition, and other physical or environmental stresses. Unfortunately you may have to go to a doctor to figure out why you're not having your period. It doesn't mean there is something wrong with you, but its better to make sure there isn't. Some women are just irregular for no rhyme or reason.
If you are sexually active you might want to take a pregnancy test, just to make sure you're not.