Not sure how much damage it would be doing exactly...but I'm pretty sure it would be significant. You might have some type of ADD condition. Were you overly hyperactive as a kid compared to other children your age? Were you a daydreamer, zoning out in class? Did your report cards seem to repeat the same thing over and over through the years? (even when you were trying?) Moments of brilliance but typically underachieving? Not saying you can diagnose yourself, it just might give you an idea.
Might be worth looking into, the exact reason for ADD is unknown but some stuff I've read points towards having lower dopamine levels and/or not releasing the amount of dopamine (relatively) that other people do for the same activities. If you think it's a possibility, think about making an appointment with a good testing psychologist.
Have any chest problems? Can't imagine smoking that much would be good for the lungs.
Just quickly from wikipedia -
If you've cut back or quit smoking weed since starting your methamphetamine habit, some of the 'feeling healthy' bit might be the fact you don't have the bongs in your system. Not sure about everyone else but I feel anything but healthy when smoking bongs regularly. When I get to the heavy chronic use stage it even decreases my appitite and makes sleeping harder (waking up in the middle of the night for a bong for example)
Maybe you can take a week or two off at some point? Do you have any holiday time you can take? You'll probably feel like shit for a while but at least it would give you a baseline mind state to assess things at.
Here's a 'getting through amphetamine withdrawal' pamphlet if you decide on having a break -
http://www.meth.org.au/fileadmin/downloads/Amphetamine_wdl.pdf