What Causes Migraine?

i am 17, 5' 9 and 11 stone. I was on the pill a while back and suffered a severe migraine and was advised that it could cause blood clots and ultimately lead to a stroke. I went to the clinic and changed this pill to cerazette, a pill which to my knowledge is a mini pill and can not lead to such side effects as previously mentioned. I have been on cerazette for about 3 weeks now. I was also told that it could cause 'spotty skin'. Today, I visited the doctors for acne cream or antibiotics, which I suffered from before taking either pill. I was prescribed Oxytetracycline tablets, and told to take two a day. I am now unaware whether they are going to make my cerazette pill ineffective. I would like to continue taking both cerazette and oxytetracycline tablets. Although would my skin continue to break out whilst using acne antibiotics if i am taking a pill which can cause bad skin? and would the pill not work? If so, I'd rather only take the oxy. tablets and clear my skin up, and go back on the pill when its better. Would this make it bad again though? Thank you for your time and help.