I did some cocaine and now have mild chest pain over the left side. i won't be touching the drug again but just wondered, should i seek medical help ?

Possibly: It is not uncommon for people to experience chest pain from using cocaine. If you regularly use, I would be concerned about your heart. If it was a one time thing that may be less likely. However, I still think that it would be a good idea to get it checked out in order to determine your baseline health whether you plan on using again or not.