ok, call your doc asap. i was on a med for depression once and after taking it for a while, it just switched and i got super depressed in a really bad way. you may need to change meds right away. don't do anything drastic, right now, with the lack of sleep and the chemicals going crazy you probably feel like you are on drugs. haha, i say this after not sleeping for two days myself. hang in there on the sleep. i have found that a klonopin before i go to bed really helps. i normally can't sleep bc i get too wound up or just brain chatter that won't stop.
exercise will help, it can raise serotinin levels. thirty minutes every day. fiber can help remove toxins like excess hormones. volunteer work helps balance things too. i like to go to helpothers.org when i am feeling really blue. it warms the heart.
my advice, call the doc for an emergency appointment, sometimes the meds start working against you, esp with a weight change or lower body weight. another thing that really helped me, i got two cats :) it seems silly but on the worst days, they can get you through. just something to cuddle on. go to the humane society and get a little furry friend. they use animals in therapy all the time. unconditional love :) and if you get a kitten, you will end up laughing so much.
good luck sweetie, hang in there. my worst was in my twenties, im in my thirties now and it's much better. really try to do the exercise, yoga and meditation if possible. they will help balance you a lot.