How Can Irregular Periods Be Treated?

Hi this is sneha, i am 26yrs old and married. i used to get my period in 35 days. for the past 2 months my periods are irregular. I got my period on jan 3rd and i was supposed to get in february but i missed. I consulted doctor and conducted pregnancy test but it was -ve. I got my period again in march 3rd aft 60 days. during that time i was suffering from urine infection and was taking anti-biotics for 15 days. after medication i had normal sex and again i missed my periods. i was supposed to get it on april 1st week but didnot get till now. i had pregnency test on april 17th and april 25th. both the result was -ve. Is there a chance of pregnancy or is it because of some problems with the cycle.