Semen quantity doesn't always factor in to semen quality. Just because a male is able to produce large amounts of semen, this doesn't automatically mean that there is a high sperm count. Only a fertility specialist can determine this factor.
There are males that are born with a consistently low sperm count. There are medical treatments available that can encourage positive gains in sperm count. There are everyday toxins in our environment that can very much affect sperm counts. These environmental factors can range from toxins, to infections, to chemical exposure.
Emotional well-being can affect sperm count more than many would imagine. A poor state of mind leads to a poor state of health quite often. Health reasons can factor in to a negative sperm count, especially advanced age can have a negative effect on sperm count. This is a fairly new find in medical science.
Sperm counts in males who ejaculate via sexual intercourse have an at least 70% higher sperm count than those who ejaculated through masturbation. The quality of the sperm was also healthier through intercourse as opposed to masturbation produced sperm.
Physical damage is one more issue that can affect male sperm counts. The scrotum can handle injuries without causing trauma to the testes, but if the area is hit hard enough, this trauma could very well crush the sperm producing tissue within the scrotum and testes causing lack of sperm production. This sort of injury could be temporary, but has been known to be permanent in some severe cases.
The best way to determine any sort of fertility issue is present; especially sperm count questions, it is always best to consult your primary care physician who can in turn recommend a fertility specialist who will better solve this health issue for you.