I’ll throw in another vote for soy.
About two years ago (at 36) I had the acne start up and my periods, which hadn’t bothered me too much for 20 years suddenly got much more painful and heavy. I never had a zit problem as a teenager, and it definitely seemed tied to my cycle. Several months ago I started adding about 30 grams of soy protein to my diet, cutting down on dairy at the same time. My skin has gotten much better, and my period cramping has decreased quite a bit. You might want to try it and see if it works for you before blasting it with tetracycline, which can have all sorts of nasty side effects (I lost hair and felt like I had the flu for two weeks when they put me on it).