when your pregnant can you still bleed?

Hi,
Welcome to ehealthforum,
It is not uncommon to see women getting pregnant while being on birth control. Nausea and mod changes are common symptom of early pregnancy. Few women can get period like bleeding during first few months of pregnancy (decidual bleeding). This bleeding is usually lighter than your normal periods. It occurs from the uterus endometrial lining bleeding due to hormonal changes (from the part of endometrium that does not take part in formation of placenta). Once the entire uterus gets filled with the growing baby, the bleeding stops.
The low back pain usually occurs due to stretch effect on the supporting ligaments of the uterus (as the uterus grows with the baby growing inside it).
If you suspect to be pregnant, you should consider visiting your doctor/gynecologist for a thorough examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). Drink plenty of water. Take adequate rest. Maintain healthy diet.
Take care.