In the Ayurvedic science, Spring is the time where our kapha quality is at the fore - we feel sluggish, congested and tired. During this phase we need to step up our exercise to counter-balance this draining feeling and take in pungent and bitter foods that stimulate the body. This lethargy soon burns off as the sun arrives and is replaced by the fiery qualities of pitta. Just as we feel 'in bloom', so does nature - long daylight hours, warm temperatures and myriad colours and shapes of flowers, trees and wildlife.
We can address much of this through our diet. If the heat is getting to you then try to avoid spicy, sour and fried foods. Cooling salads and vegetables are ideal during this time. Replace the winter staples of coffee and heavy red wine with cool drinks and herbal teas such as peppermint and liquorice.
You can keep cool in sport by training early or late in the day, or take to the water for a refreshing swim.
If you find your sleep is affected by heat at night then try sleeping on your right side to stimulate breathing through your left nostril - this encourages a more cooling energy flow and can relieve insomnia.
If you're struggling to breathe as a result of allergies this season then try a nasal wash (neti) every few days to rinse irritants from the nose.
In your yoga focus on using your breath to help cool you during practice. A breathing exercise you may like to try is sitali - sticking your tongue out (curling the sides if you can) and breathing in and out through the mouth for 5 - 10 cycles. As we transition from the fast pace of spring (where sun salutations and dynamic practice is stimulating) into the energy-sapping heat, you'll find that a slower practice suits better. So reduce the speed and duration of your movement and focus more on static poses.
For more information on Ayurveda and Sport see John Douillard's book 'Body, Mind and Sport'.