On a short term point of view, its better to keep this job.
But on the longer run, I think you should consider finding another job that you'll be able ot do for a long long time. I mean Carying those things is probably a b!tch..
Doing it regularly may F up your back, spine, cervical discs or whatever else.
You're proabably still young, so you might wanna take a risk now, and "secure" your futur.
:
: