You're not going to get a professional diagnosis here, but low self-esteem and depression can go hand in hand; self-loathing, withdrawal, below-typical performance in work or school, all can be indicative of depression. Also, males tend to respond to depression by turning to alcohol ..
.. which is a really self-defeating behavior pattern, because while the alcohol provides a short-term lift, its a depressant, so your mood the next day will typically be lower than your mood prior.
So, all of those things suggest to me that you might have something to watch and/or think about, at least.
If nothing else, prolonged negative self-talk (low self-esteem) can induce depression.
Some other things to think about, though:
1. A lot of people struggle with the transition from being the big fish in a small pond (straight A student, star athlete, etc, in high school) to being an average-sized fish in a much bigger pond. A 2.8 in one of the best universities in a country of 300-million-plus is so far above
average that its not even comparable! So, feel free to work on improving it, but don't beat yourself up for it.
2. Loneliness always sucks .. but its also much easier to make good friends in college. Some of those "fast friendships" the first semester of freshman year are forged in desperation. None of mine survived in the long term, and I certainly saw a number of spectacular crack-ups! However, I'm still very close friends with a number of people I met in sophomore and junior years - some fifteen years ago. So, if you've got a few close but not too-close friends as freshman year winds towards a close .. you're probably right about where you need to be. Second year will get better.