Changes in semen quantity or composition is a common issue, and in order to fully address your particular concerns, it is important for you to make an appointment to see your doctor
. He or she can obtain a more thorough history, as well as perform a physical exam and run any tests that are indicated.
Having said that, many things can change the composition of semen. Diet is one of these. Depending on the amount of fluids you are taking in, this can alter the liquid content of your semen. For example, if you are dehydrated, the semen can become much thicker and globular rather than watery. On the other hand, if you are drinking lots of fluids, the semen composition can be much more of a thin liquid. Certain supplements and medications can also alter the appearance and composition of your semen. If you have recently started taking any new oral agents, this could be having an impact. Along similar lines, changes in food intake, minerals, or vitamins can play a role in altering semen composition. Because sperm makes semen whiter and thicker to some degree, if there is less sperm content in your semen, this could also make it more watery. If your testicles are experiencing extreme heat (as it sounds like they are), then sperm production will decrease and the above change will occur. Likely, this is what is happening in your case, and you are also likely dehydrated from football practice and the high temperature as well.
Again, in order to address your particular situation, it is best if you speak directly with your doctor.