Hi Yowie
you can tell them that you want to try your DS one day a week first to see how he gets use to it. Most childcare centres will let you do that (well most in my areas allowed us to put 1 day a week).

At first DD was crying too but she's very much use to it now. It only took her 2 weeks (2 days) to settle in the new one and she doesnt cry at all now.

I must warn you though the first few weeks will be hard because they will be clinging and crying like theres no tomorrow but they usually settle once you leave, but they will get use to it and grow to like it.

I think you definitely need that time off and rest up.