Thanks for your helpful info.
You could be having something called " an exercise or exertion induced headache
". These types of headaches are mostly caused by dehydration associated with exercising.
The blood vessels on the left side of your head are inflamed by the dehydration which causes pain / headache by stimulating the nerves within these blood vessels.
Part of the trouble is that if you wait until you get thirsty while you are doing exercises,you're actually too late, and if you drink too much in one go your body won't be able to absorb all of it.
If you really want to treat your body right you should try to drink small gulps frequently, particularly while exercising.
Then again, if you're fully hydrated when you start working out you should be able to go at least one hour before dehydration actually becomes significant.
You should make sure that you keep yourself hydrated with plenty of water (and not juices only) and also take electrolyte supplements like gatorade during exercises. I am sure this will take care of the headaches. You can even take a pain killer like advil, if the headache is severe enough to interfere with your daily life.
Try to cut down on your coffee intake and alcohol, if you take them frequently.
However, if you continue to have the headache, you should see your GP for a clinical examination to exclude other common causes like sinus inflammation, eye problems etc.
I hope my answer has helped you.
Please remember to rate my service positive once you have all the information you need. If you have any other questions, please ask me – I’ll be happy to respond. Thank you!