Pregnancy / Conceiving / Smoker / Mother

It took me 3 years to get pregnant while i was smoking and gave birth to a healthy baby .. Now im planning to conceive but i am afraid i cant .. Just to let you know , i used to have irregular periods yet after 3 years unexpectedly i was pregnant .. Any reasons why i cant conceive when i want to .. And what if im pregnant , would smoking does any bad harms .. What are the certain chances ? #advicepls