My period is being funny and protected sex question?

[mDeHe'sgirlm]

Okay so i've had my period for two years now and its regular during school but when summer gets here i don't have my period all my signs of it coming shows up like acne, hungry all the time, but it doesn't show up. What could this be? My other question is that i'm a virgin now but my boyfriend and i are thinking about sex and i want to be on birth control but if i go on birth control to regulate my period will it still protect me from pregnancy the same as if i went to the doctor to get birth control specifically for birth control? Is it less effective?