Chest tightness, can be breathing difficulties, like shortness of breath..this could be an indication of an allergic reaction...other signs and symptoms to look for would be a swollen tongue and / or a rash on the torso...if you are experiencing these type of symptoms than you are best to stop taking the
amoxicillin and contact your Doctor or Pharmacist for further advise.
As for the nausea and vomitting, amoxicillin can be taken with food and should reduce the likelihood of future occurance....