i think it is normal to feel exhausted after you've taken on new responsibilities. and your new job is up there for being responsible!!

but just because it's normal, doesn't mean you should just put up with it. i think there will be a period of adjustment, but there are other things you should look at too. are you getting enough sleep (or are you finding it more difficult now to "switch off" after work)? exercising by any chance? managing to eat right? are you still doing pleasurable things when you have days off? i'm not talking "big" things like seeing friends... but just making some time to sit outside in the sun, rather than feeling that exhaustion in your body and staying inside the house?