I've stop smoking cigarettes for 4 months now and im not on any contraception and im not getting pregnant what could be the problem?

Inpatience?: Congratulations on stopping smoking! i don't know how long you've been trying to conceive but it takes an average of 6 months to get pregnant ; generally is of no concern unless you try for a year without conceiving. If you're having problems after a year then you ; your partner should be evaluated. There are many possibilities but about half the time the man has a low sperm count- a simple test.