First time mum to 6 month old baby.
I love it, but wow, it's hard and so much harder than I expected.
I thought the baby would feed, sleep repeat. Wishful thinking. 
It's so tiring. The lack of sleep is a killer, little time alone, little time alone with husband. Little time to wind down.
Constant worry about your baby, are they well & safe.
The worry of wether you are doing things right, is your baby doing what it "should"
The worry of if you're a good mum, are you as good as other mums.
Of course all of this is completely worth it when your baby smiles at you, laughs at you and their little face just lights up when you enter the room!!!
I may be completely alone in my feelings (in which case, I will start to panic)
But what does every one else find hard about being a parent?