Lack of sleep. Doesn't get easier either as they don't grow out of it, you stay awake worrying about them.
Like FOX says lack of freedom, I can't even go to the toilet without someone calling me (child or DH). Not being able to do or go to certain places because of having children.
Lack of respect and ungreatfulness.
Never being able to be ill and rest
My body is ruined wet myself on a trampoline
Finding it hard to be a full time student and follow the career I want because childcare is so expensive
Damned if I'm a SAHM OR Working
The list goes on...
But I wouldn't change it for the world I love being a mother and there are a lot more positive things than bad, the unconditional love, all the firsts, being proud, little milestones and big ones. Don't focus on the worst things and look at the good. 