I only have time to sleep a few hours each night due to heavy schoolwork/job. how do i manage with this constant lack of sleep?

Poorly: At your age, sufficient sleep is really important. If this go eson for an extended time it can take a big toll. In an emotionally/physically strong person it can be managed for awhile w/ excellent nutrition, good use of rest periods and stress mgmt skills. Otherwise, not. You may need to make difficult - even impossible - choices. Talk w/ school/work people about the issue, they may help some.