Hello joe,
I'm in quite a similar situation like you, I'm 22 now and in 4th yr of med school and intend to do the same as you. Infact i had almost quit med school this yr for aerospace enginnering but my father forced me not to do so. In my opinion you should go ahead for PPL righ away and see for yousrlef how u like it, If u still like it then get yourself on track for commercial flying but dont quit your job untill you're sure to get a job in flying. let us know what did u decide. regards
ssw
P.S. I joined this forum just to respond to your question