30 years old and wanting to go back to school and have 3rd baby soon-Is it possible?

Here I am 30 years old.  Ok career going, but wanting to do so much more.  I keeping the house fort ok too.  I've gotten the hang of picking up after my two boys and myself,cleaning, cooking,organizing.  Hubby does his own laundry, thank god!  My boys are 3 and 4 years.  Finances are ok, big car note will be paid off next year.  So now that I have everything situated, I'm thinking of a 3rd child!  I also want to go back to get my Masters!  I'm crazy, I know.  I really don't think I can do both.  But people have surprised me before in what they have been able to accomplish with kids, so it gives me hope.  I've taken on the belief that contraceptive pills are really bad for you.  I think it causes breast cancer, though, no health provider would say it does.  So I can't take hormones to prevent pregnancy and well, sex is complicated for me.  After that 3rd baby is produced I'm tying the tubes and saying good bye to complicated sex. Which is a relief for me.  I also want to prevent cancer in working on research projects so I know that my life would be very hectic if I had a third child.  I ultimately have left my life at God's will, which is really unnerving for me, cause I don't know what to expect.  I have faith though that I'll be ok and that things will work itself out. Anybody else like me out there?