Sometimes people just can't understand what you mean when you say you're tired. Has your husband ever had the flu, or any other illness where he felt like he was hit by a truck? Explain to him that this is how you feel every day. Perhaps that will help him understand better.
If you can afford it, get a housekeeper in once a week to help you. And your older kids can certainly do some of the chores - the 3 year old gets a pass for now but should learn to put away his/her toys.
And....forgive me for suggesting this but I think it's important for you to be able to go to the park....what about adult diapers for those trips so you don't feel like it's a horrible embarrassment if you have an urgent need that you can't fill?
Your meds are clearly not giving you the relief you need and I hope you are working with your DR to resolve this. Have you tried any dietary mods to explore other options?