I have a single zone in my house with forced hot water only heating on one side of the house. What am I doing wrong? I have bled the pipes many times and still not heat on one side of the house
99.5% you need to bleed somewhere you haven't found yet, or you need to bleed more. It's almost always an air bubble.
0.3% there's a misadjusted valve to blame. If you don't know what a balancing valve looks like it may not be obvious that it is a valve.
0.2% there's an actual blockage. I've seen a 1/2" pipe elbow that had less than 1/16" space for flow due to some VERY enthusiastic soldering (it was nearly plugged with solder), in the bizarre examples line. But this is chasing the tiny odds.
Another possible blockage - if it got really cold before you turned the heat on, there's a frozen section on the one side. In some houses that's more like 25% odds due to terrible heating system design and poor insulation.
If you can't sort it yourself, calling in a pro can make sense before things DO freeze up.
Sounds like you have a hard-to-find or hidden shut-off valve in the pipe for the back of the house that someone closed to save money. If the front of the house is heating then the pump is working, which means it is not air-locked and you separator is working fine.
If you have vertical radiators, there might be a bleed valve at a high point in the back circuit or on a radiator that is full of scale or needs replacing. If you have perimeter heat there probably isn't a bleed valve since you have a pretty flat system. So, if the back circuit was unrestricted it should have water flowing through it.
So, I believe you have a major restriction or a closed valve.