Gosh, colds are no fun--I hope you're feeling better soon!
My 2c:
For me, the trick is to get and keep those sinuses clear before a bacterial infection sets in.
Claritin-D for a week does it for me... I use the 24-hour one, but take it in the morning so I can sleep ok at night. At night, I like to use Vicks Vapo-Rub.
The D is time-release Sudafed decongestant, and the Claritin is an antihistimine, which helps with both allergies and colds.
As you've no doubt learned in open water class, one shouldn't dive with a cold, and especially when taking medicines that could wear out underwater and cause equilization issues like reverse blocks, etc.
Oh, and I try to drink lots of water.
I've never used a netti pot, but I do use a saline nasal spray that I get at the drugstore. Just basically saltwater in a big squeeze bottle.