This is really embarrassing for me at school. It started on my arm ,then my thighs ,now my neck/chest. They itch like crazy! They are pin sized red/pink bumps. What are they called ? How can I treat them?

There are a variety of dermatological reasons for what you've described from viral, bacterial, to parasitic in origin. Sadly you can never give us enough information to properly diagnose this nor does anyone here really have enough knowledge to diagnose this.

Your best course of action is to seek professional medical help. They can diagnose and give you what you need to clear this up.