I have no heat on idle and no heat while driving. It was no heat on idle got my oil changed and now no heat at all. :(

The oil pressure drop indicates more problems.

Oil pressure drops to zero at idle on 2002 GMC Envoy after ...

www.fixya.com/cars/t7880379-oil_pressure_drops_zero_idle_2002_gmc Jan 18, 2011 - You could have three possable problems that I can think of. 1) Your oilviscosity is too low and you need to change it to a higher level. A 5w/30 .

Before test use premium fuel. 1/2 tank. Change engine oil to lower co2 slightly and make sure engine is heated up drive in low gear for a few blocks to revv up motor for a while. Then run test again.

Ok Run,s smooth when WArm ?Check thermostat change it or light comes on using to much fuel so replace the oil And Filter cause you have lot,s Of GAS in OIL so Replace it then Check to see if YA HAve Antifreeze in OIL see when ya Change it Ok See if ther is some If Not change thermostat ASAP ya can wreck the HEADS ON the VAN Over HEat them

Usually the problem with no heat and overheating is low coolant, thermostat, or a faulty water pump impeller.
The radiator may not be full of liquid coolant, or the pump may not be moving the coolant thru the block.

may be the oil pump is not working properly or the water pump is not working

check engine on? if so have a diagnostic run on it .

This seems pretty normal. So long as the pressure does not fall while driving, you're good.
When Idling there is very little stress on the engine, and it requires little oil pressure to maintain.
Additionally, the pressure is directly related to the rpm of the engine as the oil pump is driven by the engine. As the rpm increase, so does the pressure. The pressure should be stable at a given rpm.

The pressure on the high side is good. On the low side is adequate (idle). You did not say how many miles, but the only way to change this is to rebuild the engine with new bearings and seals. I don't think that's somthing you want to do. Sounds fine for now. Leave it alone.
Don't fall for a new oil pump. That is very rarely the issue.

This is normal,after your oil heats up it actuallt gets thinner,unless you are dropping below 10 lbs or dropping into the red on your gauge it is probably not a problem.Remember to change your oil on a regular basis to keep your oil from breaking down and causing engine failure.

change oil pressure switch it' should be near the oil filter

Is it on when you are driving, or only at a stop when the car is idling? If it is more than at idle, I wouldn't drive it, as the engine may not be getting enough oil to lube it all and to help it stay cool. The oil pump needs to be changed in that case. It may be a bad oil pressure sending unit also.