I have a history of several mild concussions. since then, every light bump on the head makes me feel like i'm getting another one ( symptoms return for a time). are these new concussions? is this pcs?

Not necessarily: What you are experiencing is probably a migrain that is triggered by the mild head trauma. the area that triggers migraine is very sensitive to brain distortions resulting from mild head trauma.

Clarification: The "light" bumps are not concussions, but you seem very wary and anxious about this. You really need to get some counseling to allow you to feel more comfortable and confident. Chronic post-traumatic encephalopathy is relatively uncommon, even in pro football players. If you need to discuss further, a virtual consult here onsite may help.