Depression is common after a miscarriage, and you can be treated for it, through therapy and/or medication. Also, some birth control pills can make you depressed as well (not all, but some). B/C pills can regulate your hormones and moods, but you need to try many different ones to find one that doesn't make your mood bad.
I would start by a visit to the doc (gyno or general pract.), who can do a sort of screening for depression and refer you to a psychiatrist or psychologist (you usually need a referral for insurance purposes). She can also prescribe you some birth control to help regulate your hormones, just realize that you might have to do some switching around to find the one that works best for you and helps your mood the best.
Just make sure you take care of yourself!! Tell the docs what is wrong and be as honest with them as you are online. They need to realize that its a serious problem and you deserve help.