I don't know about what can influence period regularity - but the "boobs thing", it is not really true that you don't have them. Some - albeit very few - women have those extremely extremely small breasts like you do. And there is absolutely nothing wrong with that, and no problems, neither love-wise nor nursing-wise.
I hope you will be so pleased when you really feel your breasts have everything that it will make up for the (understandable) worries you have had about it.
I think it works that way - because my wife has same size as you. Really you shouldn't believe the others are better than you. They just have more fat tissue - but you still have it all. To someone who likes you, you are actually more fascinating because of that, because the magic of your breasts is not buried under a lot of fat, but just sitting right there, smiling and twittering ;o)
Also, at 19+ the boys should be much better able to "handle" you as a man, even if you are mega shy about it. They will have a much better understanding that you just want to be sure that you are okay... instead of thinking that you don't like them, if you are a little shy and reluctant ;o)
So, should work out fine in the end. Hope you will so fine and happy ;o)
Best wishes to you!