Alysym, I am in the same boat, 2 yr old DD and a 3 month old DD. No family help nearby, and hubby working 18 hr days at the moment so no help there either.
Feel knackered the whole time, and DD1 can have me yelling and feeling crap within 10 mins of her waking up in the morning.
DD1 is doing things like tipping her food on the floor, pulling poor DD2s hair when she's feeding, deliberately scaring her by screaming really loudly/high-pitched etc.
I have found it easier to not shout and tell her off for these things, but instead I just do what I have to to stop the situation. E.g. take her food away the second I think she is full and starts to think about messing around with it, or when she tips her milk on the floor deliberately, I don't say anything at all to her, just wipe it all up and say 'Mummy is sad now', and nothing more. If she hits DD2 I pick up DD2 and move her away.
I find it more stressful to shout at her, or explain things (she understands completely but does it anyway), and better to heap loads of praise on her any time she is good.
It is crap though, and completely knackering. You have my empathy and sympathy. We just have to remember there are plenty of mums going through exactly the same thing, to moan with share tips and experiences with, and it will, one day, get easier so they tell me, it better bloody well do.