off depo for a few weeks, How soon can the blood test tell

Hi,
Welcome to ehealthforum,
The bleeding that you experienced after missing the Depo shot could have been the withdrawal bleeding. If your fertility/ovulation has returned immediately after stopping with the Depo shot use (after missing the shot), and if you have been sexually active without protection, a chance of pregnancy resulting in immediate cycle is a possibility (women have reported pregnancy in immediate cycle after stopping with hormonal contraceptive use). The symptoms that you describe could be suggestive of pregnancy possibility. Wait and watch for your periods. Look out for development of any other new symptoms if pregnancy is suspected. 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.