Help, iM a 19yr old girl & my mechanic gave up on my car

My car has been acting up for quite some time now. Here's what it does:

It shakes quite a bit when its in drive. Only time it doesn't shake is when its in neutral.

The check engine light has been on for probably a year or so now. My mechanic got it to go off for a day or two but then it came back.

Sometimes as I'm taking off, my car looses power and it almost feels like there's no gas going through it. The RPM's sorta get stuck in place and my car is basically moving very very very slowly. It feels like its stuck in gear or something.

To get it moving right, I either have to let go of the gas a lil and then step on it again. Or I have to "really" step on the gas which causes my car to "instantly" take off. I say instantly 'cause it literally accelerates like crazy if I do this (it causes your head to jerk back a lil). When ever I use this approach, the RPM's usually almost red line and then it shifts gears and drives fairly normal after that.

The problem happens very often lately but it used to mostly happen whenever I was going up hill.

I've also noticed that now that its acting up more, it seems to burn up gas alot faster. I'm at the gas station quite a bit considering I'm driving a 4 cylinder car.

My mechanic changed the sparkplugs on it and thinks it has something to with them still. But he says he can't be sure of whats wrong with it. He has tried plugging it in to the "computer" (sorry, I'm not sure of what this machine is called exactly) to try and see if it'll tell him what's wrong but apparently it wont tell him anything is wrong.

So my mechanic pretty much told me to try taking it to someone else.

I'd greatly appreciate any ideas, tips or any help you can provide me.
Maybe a certain shop that specializes in Hyundai cars or a shop that is fair priced and near my home. (I live in Southern California in the city of Ontario)

Thanks In Advance :D