Worried about 3 year old.

Hello parents. Don't really know how to start this so just gonna let me hands type. My wife and I have 4 kids, 2 months (girl), 3 (girl), 5 (boy), and 6 (girl). Our 2 month old is my wife and I's first baby (also my only). I came into their lives about 3 years ago (before our 3 year old was born). Our 3 year old has a separate father then the older two but he isn't around. I've been there since mid pregnancy and when she was born. Our 3 year old has always been the "black sheep" of our kids. The oldest two were fairly well mannered, I'd say typical kids sometimes listen sometimes don't. Our 3 year old though. She has always had an attitude ever since I can remember. She was very colicy when she was an infant, which I know isn't an attitude (or her fault) but I wonder if all the screaming and fussiness didn't help. At about a year when she started to move and talk she would fight her older siblings over everything. If they had something she wanted she would scream and/or bite them, all the time. My wife's grandparents spoiled her a lot which didn't help. She has always been very advanced for her age (knew all her ABC and could count to 10 right at age 2), she always knew when to be sweet to get what she wanted. Never wanted to share with her siblings. If she didn't get what she wanted in public she would throw a pretty bad tantrum sometimes, throw her self on the floor or scream. I've often read parents say they would just start walking away and their kids would get up and follow. Not our 3 year old. We stopped doing that after a few times because she didn't follow, ever. She would either stay where she is and play or get up and start walking the opposite direction of us. She really didn't care if we were there.My newish job has me working a lot, 5 days a week 10-14 hours a day so I haven't really been there to see how bad it's gotten. Today was swim practice with all the kids, the last time we had swim practice our 3 year old threw a pretty bad tantrum because she didn't want to get out. Today was bad as well, like I've never seen her this bad, hysterical screaming crying and flailing. The weekend before I talked to her about it as well, told her that if she wants to continue to do swim lessons she needs to not act that way, it isn't appropriate and doesn't make mom and dad happy. She acknowledged it when I said it to her but I knew she was going to freak out again. Told her she doesn't get to do swimming anymore and she didn't seem to care.Two weeks ago my wife took our newborn in for a check up, when it was time to head back our 3 year old freaked out because she wanted to continue to play with the toys that were in the waiting room. It was so bad that the doctor had to carry our newborn so our wife could get our 3 year old. It's embarrassing and frustrating that it gets to that point.Before our 2 month old was born family and friends kind of jokingly said to make sure to watch our 3 year old girl around the newborn. We all laughed but sadly we were all kind of serious. I would be lying if I said my wife and I weren't some what worried about how our 3 year old was gonna act towards a new baby. Which sucks to think that way about our child.We've tried hard discipline and gentle talking to. Nothing works. She acknowledges what we say but turns around and acts like she didn't hear it at all.We are also concerned some of it might be mentally. Her biological father has a lot of issues. Has always partied a lot, on 10 different medications currently (we recently asked him but try to not talk to him at all since the whole situation is just... yeah) for his mental issues which he said the doctors still can't figure out. She has a check up in November which we will bring all this up to the doctor. I'm not for medication, at least at this young. Afraid it'll make it worse because she is still so young, but I also don't want to put it off for to long in case it could help.So that's it. I really just wanted to let all this out, and any advice is appreciated. via /r/Parenting http://ift.tt/2x8PJ9e