I do think this sounds like depression. Your best bet is to see a GP and get a mental health plan, and explore your feelings with a counsellor who is trained to help you work out what's going on, and how to help you navigate it. Everyone here would love to try to offer help but no one is going to do better than a trained professional. Good luck!!!
I do agree with "the other guy" in that a proper diagnosis is the only way to go. Outside chat and advice is beneficial however.
I recall joinin gthe RAAF in 1973, I was 17yo, jetted from Melbourne to Adelaide for recruit training among many other lost souls all older than me. I was lost, I found everything daunting, new everything from haircut to clothing, environment, weather, noise (aircraft), room mates and food. Drop yourself on Mars- be similar. However, 4 years later I left that job to join a jail as a corrections officer and got that same feeling as it was yet another strange environment. After 3 years left that to join Railways investigations and the same feeling. So I began to accept that this was a combination of new places and new challenges, just other appear to handle it better.
I might mention that you are at University to achieve a goal. While its 'normal' to hang out with friends and other activities, they can easily divert your attention to such goals. It's most important to give this your best effort and only accommodate other activity when you feel the need and have the time. Some of those "friends" might not need to study to achieve a pass. I had 80+ jobs and 15 professions (due to mania) and out of those I ended up with 3 good long term friends so quality of friendships is the way to go.
Finally, there is many diagnosis you can have besides simply missing home etc (which is a possibility). eg I have bipolar2, depression and added to the- dysthymia. Dysthymia is a mow mood constant depression. It does cause crying and high emotion and that feeling of lost euphoria. Hence the need for a proper assessment.
I hope that helps.
Here is a thread that might help
Here is a thread with several links that you'll find inspiring.