i dunno what to tell you about the cause of the pain... maybe see yourself an MD

but heres an idea... your lungs absorb all the possible thc from a hit in under 10 seconds... if you hold it in any longer you aren't getting anything but o2 deprivation... so try holding your hits for no more than 5-10 seconds MAX, since thats all you need.. and see if it helps

if the pain persists and / or gets worse, then i would suggest a trip to the doctor asap or at the very least stop smoking and start vaporizing