File a motion for change of support as fast as possible. You’ll probably need a attorney for that, unless you’re familiar with your county’s court house procedures. It will take time to have an adjustment hearing, but when you do it should be retro’d back to your filing date. You can’t depend on the FOC to make any changes.
The PT thing might be hard to get a judges approval. You best strategy is to convince him that you need the training to bring your income backup to where it use to be at.
By the way, $1100 does sound high for just one kid. I pay $1500 a month, but I have 3 kids with a income of 67K a year. You either must have a large income or work a lot of overtime. Check with your state CS guidelines because here in Ohio overtime and bonus must be average over a 3 year period.
Good luck bro!