Unless your doctor has told you otherwise, it is fine to resume your normal daily activities and exercise routine after a miscarriage as soon as you feel up to it.
After a first-trimester miscarriage, your body will return to normal fairly quickly in most respects, and there is no reason why you should not go to the gym or do your normal exercises unless your doctor has advised against it for some reason.
Your doctor may advise waiting a few weeks to exercise after a later or full-term pregnancy loss, however, because the body needs a longer time to recover after a longer pregnancy.
Source:
American Pregnancy Association, "After a Miscarriage: Physical Recovery." Oct 2003. Accessed 1 Dec 2008.
