I tend to isolate and withdraw myself from my circle of friends because I don't want people to know about what I feel then I'd end up feeling alone and think that nobody cares. Is this normal?

I have done that before and I wouldn't say its normal but I wouldn't say its not normal either. Many people experience this but its best if you reach out and find support so that you no longer have to isolate yourself, and so that you can be happier.