I don't think it affects your testosterone level. But if you want to boost your testosterone levels, rigorous exercise will help.
Masturbation shouldn't make you feel tired all the time. Maybe you aren't eating right or getting enough exercise or sleep. You can over stimulate yourself with too much of a good thing, just cut down a bit from time to time.
Consider the amino acids and other nutrients lost when you spooj, also the endorfins released in the brain at orgasm -- the ones that make us sleepy. Nutrition and some self-control may therefore be the answer. Make sure you're taking a good multi-vitamin and restrict masturbation to once a day. If you have the balls to commit to a week of abstinence, do that: I have noticed an incredible increase in energy and pep when not jizzing every day.