I am going to get flamed for this, but i dont care, i do think that if you are a SAHM, then it pretty much is "your job". That is how i view my childcare responsibilities. I do think it stops there though, and the housework should be shared fairly, but realistically, it is the SAHP that gets to do the most of it because they are there!
My DP is a perfect daddy, but he leaves most of the parenting to me during the week.
We have to remember that the OP DH works seven days a week, AND studies. And yes, SAHP is a 24/7 job.
I dont think getting on feminist high horse is going to help. But i do think that OP just needs to point out that she does need a break, and the very fact that even though DH studies too, the change of scene he gets when he comes home and the chance to spend some time with DS IS a break for him.
With some straight and honest talking i dont see why this has to be a major issue. But i think putting up and shutting up isnt the way to go, because if you dont say anything, how is DH supposed to know you are unhappy, because lets face it, if someone around me opts to do the lions share, i'll bloody well let them.