What can I do to help treat depression and anxiety? I have an appointment with a psychiatrist in a month, but I'm feeling really low right now.

Exercise . Think of 3 things you are grateful for each night or that went well during the day. Don't isolate yourself. Eat a well-rounded diet that includes b12, folate, (folic acid) and omega 3 fish oils. Surround yourself with positive people. Walk 20 minutes a day. Connect to a higher power. Do something you enjoy 10 minutes a day. St. Johns wort is an over the counter supplement that can help mild depression.
Psychotherapy. Talk therapy is very effective for anxiety and depression, and studies have shown that the insights and skills you gain this way effect physical changes in the brain. Here's an article outlining types of depression and various psychological approaches to treatment: http://davidgodot.com/depression/
Be tough. Dr. Baker has given you good advice. Confront any life situations. Get out of any abusive situation. Do not accept verbal abuse. At age 19 work very hard to train for you future career. You do not need a romantic relationship right now to be happy. Try being kind --even a nice word-- to others even when it is most difficult.
Many things. Exercise- even brisk walking helps, ideally out in nature. Meditate daily (http://tinyurl.com/nop2pw6). Talk with friends and family/see a counselor. Take a good B complex that has the L-5-MTHF form of folate (folic acid). To relax try Tulsi tea and magnesium glycinate. 5-HTP (300 mg at bedtime) and Meriva (a curumin extract) can help. Try EFT (http://www.eftuniverse.com)- many instructional videos on youtube.
Consider fish oil. A high quality fish oil (Costco's is good among others) in maximum tolerated doses can dramatically improve mood and it is very safe. It could help other antidepressants to work. It is worth a try and you can start it yourself. All the other suggestions I have read here are good as well. People are applauding your willingness to seek help and are behind you in your efforts. Good luck!