R.,
You have NOT spoiled your grandson. You have spoiled your daughter. : )
You may have to get creative with this one. I don't know what your daughter is doing when she is 'home' when she expects you to watch her son while she is there. At 5 months he is certainly too young to 'put down' and just 'leave' and you are right - I feel - for doing this!
She needs to step up - but at the same time, she needs to be, well, responsible. She is his Mama. It sounds like he has imprinted on you.
Set up a time to talk to her - that might help. So you are both calm and she can 'hear' you without being diverted. She's 20. She may not be mature enough for this conversation, either, so don't expect much.
Another route would be going to YOUR doctor. Yep. Get an appointment. Get a prescription that says - more sleep - more regularly - more often. Even have him give you a script if you feel like it - melatonin works wonders (and it is OTC ; )
You have to stand up but in a way that empowers the rest of the family to take over a little at a time what you have freely given.
What would you (God Forbid!) do if you found a lump in your breast? You would have to go through all this and MORE. And not only would they have to pick up the slack, they'd have to do even MORE around the house than they do now.
Another avenue would be Flylady.com / .net She's got ideas for cleaning that will take the load off you and help you get/keep things in order without going nuts.
I wish you luck. I hope you don't have to use subterfuge. But it really isn't if it is your health involved.
And take the babe with you to the appointment. : D
A baby sling might help you a LOT, also, if you don't have one already. DD can pick up tips on how to wear it.
Good luck!
M.
PS: other ideas, just have DS waking any second now! And YES, I carry him everywhere too! Good for you!