1996 Chevy Cavalier Won't start - engine backfires

This winter has been a killer, she tries to turn over but won't start. On the coolant side in the upper radiator hose that goes to the thermastat housing, while the car is running, it is easiy to compress like there is a flow problem. I have changed the water pump and thermostat and flushed the engines cooling system. Did not work. I have replaced the spark plugs with Bosch Plat +2 that are gap set. While trying to get her started it is like the engine builds up compression and I have to take some of the coolant out of the resivior because the coolant doesn't seem to be flowing through. If I do get her started she runs very ruff and with each gear change loses power but at times seams almot like something opens up and I get the power back. While she has a loss of power when I get to the lower gear changes you can hear some small engine backfires. If I am able to keep her running while driving her it is alomost like there is a blockage somewhere. When trying to start her it is almost like she is not getting enough gas but I can her the electronic prime working. Also when she is running in idle it is like she is missing or just real rough. If you turn the heater on she will try to die. Another wierd sound is while driving her it sounds almost like water going through pipes under the dash. PLEASE HELP? I cannot afford to go out and get a new car.