Any tips to deal with tension headaches?

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Once in awhile I get up with these nasty headaches that start off slow and gradually increase through the day. When I try pinpointing the location where it starts, I can normally find it is along the middle back and trace it to the shoulder, along the neck muscle. It seems to only affect one side of my head though; usually the left side. It seems to settle above my left eye (the is swelling there) and my eye get very tired and sore. At times the pain can be quite bad to the point where I can't do much. So far I've tried medicine and massage therapy (which is great but gets expensive). I can deal with them when I am off work by laying down and relaxing for a few hours but when I have to go to work it aggravates them (working in front of the computer all day). I think these are tension headaches although I was told they can also be migraines. Anyone out there have any tips o how to deal with these and help at least lessen the pain so I can get semi-productive when they hit?