We r trying to conceive since last 3months but no result.but i have increasing pain during periods from last three months that i never had before.why?

It takes time: It can take up to a year of trying to conceive. Pain during menses not unusual, called dysmenorrhea, and bodies change throughout menstrual lifetime from age 13 til 50 it's never the same throughout. Since pain and trying both for 3 mos, perhaps if you were on hormonal contraception, came off to try, that may be reason, as a benefit of oc's is less dysmenorrhea.