I am having great difficulty falling asleep. I do a lot of physical activity. Is my difficulty falling asleep due to a lot of physical activity?

Exercise can... Excessive exercise and physical activity too close to bedtime can interfere with your sleep.
See Below. Talk to your pcp about not being able to fall asleep. Practice sleep hygiene -- exercise is one of the things to avoid right before bed time. Establish time when you would like to go to bed and stick to it; no heavy meals prior to bed time, no stimulating activities; try warm showers and keep a room on a slightly chilly side; relaxation, stress management might also help.