recently missed my period and having stomach and back pain

Hi,
Welcome to ehealthforum,
You can expect chances of pregnancy if you have been sexually active without protection, and if your normal fertility and ovulation has returned back to normal after stopping with birth control pill use. The symptoms that you describe could suggest pregnancy possibility. Look out for development of any other new symptoms if pregnancy is suspected. Wait and watch for your next periods. It is difficult to comment on your pregnancy status without examining you. If periods do not start within 10 days of expected period dates, or if you get abnormal periods, or if you suspect chances of pregnancy, consider visiting your doctor/gynecologist at the earliest for thorough examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Take adequate rest. Drink plenty of water. Maintain healthy diet.
Take care.