Not so much things about being a parent, but being a young and single parent. I didn't particularly plan to have DS so young but as a teenager I did used to feel very broody and had this idealistic image of myself with a baby/toddler and how it would be if I did have a child young.
I didn't realise that it would be so hard to see all my friends going finishing uni, starting their "adult" lives and getting interesting jobs etc. (Though I am hopefully starting a PT degree in October)
Also seeing them posting on facebook about having nights out etc, clubbing, getting drunk, etc etc. Even if I did go out I have to be back at a reasonable time and I couldn't really get drunk because I have to look after DS the next morning.
Didn't realise it would be so hard to see how DS' Dad was with him when we were together (as in not brilliant) and then letting him go off to him every weekend and not knowing how well he's being cared for etc. The conflict between wanting to keep up a relationship between DS and his Dad, (and he does seem happy when he's there) and wanting to keep DS safe and not exposed to certain things.
Also not being able to just buy everything for DS that I want to - at first when I was pregnant I was sure I wanted to just be thrifty and get the cheapest pram I could find etc, then realised I didn't want DS to be uncomfortable in a crappy cheap umbrella stroller and I wanted something parent facing etc.
Other, more general things:
That point in the day where you are just exhausted and have no more energy to deal with a toddler, and yet they are STILL UP and want you to be doing things with them. DS if I don't time things right can still be up at 11 and wanting to clamber on me and breastfeed etc and I get so frustrated with it.
(Sort of related to previous) I find it hard when I'm trying to get DS to stop doing something and he keeps going back and trying to do it 76238920 times and will not be distracted!
And then the big one - just the amount of housework etc that DS creates, and trying to do that and look after him and have time to myself. It's not the parenting I find hard, it's everything else!
Still wouldn't change him though