ive had this feeling everytime while going to school on the mrt, i travel quite far so its a long ride. the problem is when people start coming in i feel sick, like stomach aches, nausea like just wanting to puke. i dont know if this is just a panic attack or just anxiety. ive never been good with people nor socializing and making friends in school. im paranoid (undiagnosed) most of the times, always having this feeling of impending doom that people are judging me or backbiting me even though i dont know them and vice versa. it started off rarely but now its almost everyday and its affecting my sleep and my courage to even go out anymore.
Dear @idkanymore
It is good that you have reached out to address what you have recently noticed. Understandably it is affecting your quality of life and it’s clear you determined to overcome the situation.
I believe that negative thoughts of impending doom and people judging or complaining about you are occurring because of an overthinking mind. Our mind generates thousands of thoughts a day and many of these are not helpful nor true. I encourage you to start practising being more mindful of your thoughts as they arise. Put some distance between the thought and yourself by saying, my mind is having the thought, “(insert the thought here)”. This creates a space between the thought and yourself. This space thus gives you time to choose a more balanced response instead of your autopilot reaction to it.
Speaking to a school counsellor would help you too. He/she is trained to listen to you non judgmentally and provides a safe space for you to share your fears, process any issues you are struggling with and learn techniques to manage and reduce distress.
During your train journey, proactively plan what you could do instead of letting your mind wander. For example, I have seen students knit, write notes, read, do homework or rest their mind during the ride. Do consider some healthy distractions that work for you 
.
I hope these suggestions are helpful. Keep taking small steps and adjust often, to make effective improvements to your current situation. Reach out to the supportive community here whenever needed. You can get better! 
it sounds like u have anxiety of crowds, agoraphobia? Have u sought prof help?