Why i am not getting pregnant .i have 6 year old son . i am try since last year. i had 3months old miscarriage last year.?

Many reason: You need an infertilty workup if you ahve been trying for 12 months esp since you have already had 1 child call your gyn on monday for a workup- can be many different reasons.

Something changed?: The good news is that you have had a prior healthy (i assume) pregnancy before. In addition, one miscarriage does not mean that you are at risk for another one. I would recommend a visit to your OB to discuss your situation and ask about labs, an ultrasound, and setting your partner up for a semen analysis!