Headache Back of Head (left side)

I have had this really annoying ache at the back of my head on the left, which seems to be triggered by using computers or anything like mobile phone screens, etc. I am using computers for massively long hours (setting up a web design business). I have noticed it get worse, as it only takes about 40 minutes of being on the computer and it starts. I seem to be fine when not on computers. 

I am 19 years of age. 

I'm no medical professional but the only thing I think of, is it could be something to do with eyesight? From memory, I used to make a yearly trip to the opticians who always told me I was on the borderline for needing glasses part-time? Then I think it was the last time I went when I was 14, and they did prescribe me with glasses that year for part-time use. Being a typical 14-year-old, a never wore them. Would you think that's a possible cause? 

See a optometrist for eye exam. Computer & the light is very hard on the eyes. If you had glasses earlier in life & then a few years later it's time for another eye exam . It would be a good start to see if the headaches stop!  

I also meant to add that I have glasses that have a special lenses that also help,with the light glare from the computer . Ask you dr about these lenses especially made for glaring light from computers.

Yes, definitely get your eyes tested again and tell the optician you are using a computer a lot. An ache in the back of the head usually means your eyes are struggling with focusing accurately.   Dont work in a darkened room and give yourself lots of breaks to look away from the computer. Get up and do something else at least every hour, if only for a few minutes.

Dont work nonstop on a screen or you could also end up with painful dry eyes. We forget to blink when working on a screen. 

Thanks that makes complete sense. I'm no expert but that does seem to be the issue, the eyes focusing. I believe when I was doing my driving lessons, my driving instructor said about my eyes focusing not to long ago, I did pass my driving test but did slightly struggle to do the number plate which was probably a sign. I will defiantly get myself to the eye test, especially before I get my car insurance!!!