I need help with my horse!!!?

I got a new horse a couple weeks ago. When we went to the girls house to pick him up he was awesome, I climbed on his back, bareback and he was fine...we got him home and wanted to ride with a saddle and bridle and stuff, well he tacked up well but when we tried to get on him he stepped away and wouldn't let us near his side, finnally we had my cousin(who is tall) lean on him and put a little preasure on his back to see if that was his problem, and he reared up!! So we thought maybe he was just just nervous from the move. We put him in the pasture and let him calm down, I went out there and just brushed him and stuff, then my mom held him and I jumped on his back bareback again, he was fine! So we thought everything was ok. But latley he is being a frickin jerk, when I try and get him to groom him he holds his head WAY high, he pushes me all over, and he just troughs a fit. So when my mom was trying to worm him he threw his head and so she made him walk in cirlces, then she tried again and he reared again!!! (We didn't. Get a chance to worm him cause he kept rearing) then yesterday I got him out to brush him, I was tieing him to the hitching post and he reared when I was right there by his shoulder!!! Now I am a beginner rider, so I don't know what to do, I jumped back and when he came down I tied him up and made him stand there till I was down brushing him and all that stuff, he was troughing a fit the whole time. Know we do have 2 mares, who wer. Whinnying when he reared up at the hitching post, but they wernt any of the opther times.... whay is he rearing, andhow do I stop him, its dangerouns amd scary, I can't hit him on his poll cause I'm not on him, and I can't just work him after he rears cause he won't let us on him! What's his problem, I mean he's a gelding and when we seperate him from our mare he acts like a stud, and when we do stuff with him and the mares still in the pasture he is just a jerk, and no matter what if you try and make him do something he doesn't want to he rears, what's wrong with him and hpw do I stop his rearing( and I'm not flipping him over backwards so don't even suggest it) thank you!