You are lucky I've had depression on and off due to the lack of friends. I am a social and extraverted person and I just don't see why I don't have a good circle of friends. I am a college student too not some old guy or anything. You are lucky your friends have not rejected or abandoned you like they did to me. If you have any questions let me know.
Also about your depression it can be caused by several things: Have you been getting enough sleep? Or sleeping too much? Have you been under heavy stress for several months or weeks? Have your friends or family been arguing or fighting frequently (because sometimes it is environmental), Have you stopped drinking caffiene or any other substance (it could be withdrawel symptoms), Do have chronic negative thoughts about yourself or others(your self directives or cognitive chain could be negative), Did you stop attending Church, sports, or other positive events or activities that you have enjoyed a lot? Are people at school or home abusive to you? Is school boring/tedius/lame all the time? Have you started drinking alcohol or any drug including prescription drugs?
I am not a psychiatrist or anything but I believe that most depression is caused by environment and sometimes the thoughts within your head cause your mood to get worse - for example the frequency or rate of your positive thoughts such as "I did a great job at school today" "My friends think I am so awesome" may be very low and because you do not have enough of those good thoughts you are getting depressed. Psychiatrists believe that it is usually biological/physiological that is why they prescribe medicine. If your depression gets worse please see a board certified psychiatrist- make sure he is Board Certified and has tons of experience with teen agers. Also get second or third opinions but first before going to a psychiatrist - try a cognitive behavior therapist who practices behavior modification and will assess you with The Beck Anxiety Inventory and Beck Depression Inventory. This way the therapist can keep track of yoru depression and see if the therapy or interventions are helping you to feel better and happy again