In the news today in the UK it is said that women in their 20's are becoming hooked on anti-depression drugs being mis-diagnosed as depression when really they just have severe PMS.

I am 25 and in the last 4 years have been really depressed, crying, moody, nasty and feeling like a big dark cloud is over me, then i will be okay again the next day. I am on the pill (Microgynon) and have been for 2 years so surely that would calm my PMS down.
Please help, what could be wrong with me? Am i suffering from depression?