What type of anti-inflammatory did you get? You can try switching to a different analgesic, like acetaminophen (tylenol), or aspirin, or a different anti-inflammatory than the one you were prescribed (my favourite is ibuprofen in advil). You can also try adding caffeine to the mix and seeing if that helps (I think they're allowed to sell combination caffeine / analgesics in Canada now, but having a coffee with your pills works too).

Judging by some quick research into the topic, the only real treatment for chronic TTH is amitriptyline which is an anti-depressant so you might have to suffer through some nasty side effects.

If it's mainly your back and neck that are giving you issues, you might consider trying to work out those muscles a little more aggressively rather than just stretching. I'm not good at isolating specific muscle groups for exercising, but I'm sure you can google it. Not sure if this'll help or make the situation worse though.

When you miss work is it mainly because of the migraine aspect of it? If so you may want to seek treatment for that instead, since it's a little different to treat and you might get away with not having to be on amitriptyline.