Hi elizamt,
This all sounds fairly familiar to me. Like you, I'm in school (which stresses me out); I take classes at night, and my job (at a university) is quite stressful during the school year. Add an already anxious/tightly-wound personality to the mix, add a chronic illness like Crohn's, shake it all up and you've got a helluva cocktail for anxiety and depression!
David is on point as far as the vitamins are concerned. In my case, I've been told that my iron and B12 levels are good, but my vitamin D needs to come waaaaaaay up. I have heard that this can help with depression, but I realize that it takes time to bring that stuff up to a healthy level. Even though my diagnosis is mild so far (waiting on the Prometheus test results and getting an MRI on Friday, so that might change), and my symptoms are probably not that bad compared to some of the other posters on here, I still find myself struggling with this and falling into depression and crying jags, and it definitely coincides with my symptoms and if I perceive that things are getting worse. It can quickly spiral out of control.
Anyways, for me personally, I would love nothing more than to manage my anxiety and depression through lifestyle changes, supplements, and more natural means, but for the time being I am trying medication to see if it helps as an extra measure while I make adjustments to a relatively new diagnosis. It's hard to think clearly when you're down, I know, but you should definitely realize that a) you are not alone in feeling like this, and b) if you are depressed, it's not for "no reason."
One more thing... For me personally, I find that this forum can sometimes be a double-edged sword when I'm out of sorts. (Other members, please understand that I value this community and I mean no disrespect!) This messageboard and its members are all great resources; you're going to find a wealth of information here and lots of great people who will understand your situation and support you. That said, if you're like me and you're prone to worrying, keep in mind that if you start looking for answers while you're really upset, you can psych yourself out even more if you go looking for bad news. 90% of the time I come here, I'm feeling pretty OK and I find lots of useful information and contribute what I can. The other 10% of the time, when I'm feeling down, however... it's pretty easy for me to start searching the boards and really making myself upset. It ties in with my anxiety. Keep it in mind if you think it's happening to you as well.