I think these have been related to stress. I also suffer from left eye migraines, have for many many years.
Some have been so bad that I seriously felt like I was going to die and said my goodbyes to my pets and hubby before going to bed. I felt cold to the touch but was hot, nauseous, dizzy, couldn't see, etc. This was after a 2 hour bike ride. Usually these appear to creep up for no apparent reason.
I am also on the computer all the time, but have RX glasses I always wear to not strain my eyes.
I still dont know why I get migraines but I do know if you get them following exercise, that your body probably requires more electrolytes during exercise. You would want to use gatorade and sip it throughout your exercise, or water with a splash of sea salt and squirt of lemon (salt is an electrolyte).
I usually do get left eye migraines when the weather changes. They are called barometric migraines. I know there is nothing that works (tried all the meds) so I just shut myself in a dark room when I feel it coming and go to sleep. Usually when I wake up the next morning, I feel normal.
If its not exercise or barometric related, good luck finding out what the problem is. I'm 99% sure mine are from stress (pinching my forehead muscles between my eyebrows together all the time). If that is possibly your case, try laying down in a dark room with candlelight and relaxing spa type music every day as if it were required.
Food is also a contributor factor to my left eye migraines. Sometimes if I have too much sugar, not enough sugar, not enough protein, etc it will cause a migraine.
I sometimes know what the migraines are from, and sometimes I dont.
Make time to unwind. Hopefully that will help.