What Causes The Delay Of Periods For 2 Months?

hello im a 17 year old girl i dont know what my sickness is . my menstration is delayed now for 2 months .. my stomach cramps sometimes .. my doctor diagnosed me with u.t.i but im not convinced . im shy to take a prg. test but i dont know what to do . sometimes my right side hurts then sometimes my left . and it also feels like i got alot of air in my stomach . i often release gas im really confused pls help. THANKS