coolant light...help!!

My car has been working wonderful until... 3 weeks ago I got an oil change on my car. The next week my coolant light came on and my heat gage was going crazy. I took my car into a mechanic who replaced the temperature gage and some fuses. My coolant light stayed off for a week, but now it is going crazy again.

It keeps randomly coming on, and I have plenty of coolant. It doesn't seem to be overheating at all.

Please help! I don't have the money to keep getting it fixed if the problem isn't solved. Is there any way to find out why the light is coming on?

Thanks!

Is your resovior full? Did u know there is a sensor in the tank that will put the light on when it gets low, or just flick that sensor a few times and should be ok. OR umplug you bat for about 30 sec to 1 minute. to reset your cars computer.