I can't seem to trust anyone. is something wrong with me mentally?

I don't think so: If you are surrounded by a chaotic social network, i would say that your lack of trust would not be unexpected and it is a learned defense mechanism. It is encouraging that you are aware of your lack of trust. This means that you have great potential to do psychotherapeutic work and overcome this. Trust should be selective and there are different levels of trust you might ascribe to others.

Trust is complicated: As with many questions like yours, the answer is bound to be more complex than something is wrong or something is not wrong. The fact is, you are worried that something might be wrong and there's a great chance that by talking to a professional you can come to a better understanding of why this has become a concern, and match your ability to trust with what you want for your life.