first of all there was no insertion of his penis. we had dry sex 3months ago. I took 2 pregnancy test which was negative. the time gap between both the test was 1 month. so its pretty good time to build up my hcg level. from last two months my period is irregular. in the last month it lasted only 2 days but it was heavy. before that it lasted 3days. 1st day was heavy. I am having this pregnancy symptoms like back pain,gas, my tummy looks little big. how can I be sure?

See your doctor. But, based on what you have said it would be unlikely. The symptoms you describe can be due to an number of things.

I agree , on the information you have told us, it is very unlikely that you are pregnant. But yes a visit to your doctor and a blood test will tell you 100 percent