What Could Cause Missed Periods And Pain In Breasts With HPT Negative?

I am 22 years old, 1m65 and 55 kg. iv last had my menses ending january 2011 n since then no. i have done one hcg pregnancy test which availed to be negative. my breasts are paining since this week. i want to know wat are these signs? i am currently taking primolut n to have my menses. must i do another pregnancy test?