Change in PMS symptoms

Okay, I am 20 years old, and I have a question on PMS.

I rarely got bad PMS before starting birth control (which was a little over a year ago) and after starting it, I got increased symptoms like mood swings, breast pain, and some cramps but not horrible.

On my last period I had the worst PMS I have ever had! My breasts hurt even just to touch them, and I had cramps that gave me bad nausea.

The odd part is that all the symptoms started a little less than two weeks prior to my period.

Why would symptoms suddenly become so much worse than they have been previous times?

I am asking this because it is now two weeks before my next period is due and once again I'm getting the bad symptoms and I don't understand why!

Any advice is appreciated!

Thanks!