Hello
I know how scare can be to have this things happening to you and you're only 12 :)
You need to talk to your adult guardian and tell this person (mother or who ever the person is) what is happening, so this person can get you an Doctor appointment.
Can be just change of hormones or something else, but is better a doctor check you out, after all this is the reason we have them :) they are trustworthy and you gonna be just fine :)
I think you have to go to a doctor asap..