What Causes Headache After Performing Physical Activities?

hello,sorry for my spelling.. for 5 days ago i was out swimming, i decided to test for how long i could swim under water, i reached 50 meter, but at the moment i got back to the surface i got a strong headache, and felt very tired..the headache continued to the next day and then was gone..yesterday i was running and i got headache instantly, after 6-8 hours it disappeared again, today when i should do push ups, i got headache again and still have it, it is 4 hours ago..what could it be?