How to deal with tension headaches and neck ache on that side?

First things first: If you are certain that your headaches are tension headaches, then the best treatment is to reduce the tension. Range of motion exercises, frequent positional changes, heat (and/or ice) and massage are often useful. Using over the counter medications no more than 3 times weekly may also be helpful. But more frequent usage, even of these otc drugs runs the risk of provoking chronic daily headaches.