Getting proper sleep. Are you getting sufficient sleep or are you not getting restorative sleep. If you are not getting restorative sleep talk to your doctor about a sleep study. If there are no medical reasons for your tiredness and a sleep study is normal, then medications such as Provigil or Nuvigil may be helpful.
Why. My first question is why can't you stay awake and focused? If there's a problem, best to get checked out and treat the cause. Healthy people don't need to rely on stimulants to perform. Any stimulant, from caffeine to amphetamines, can keep you awake. But, they all have side effects as well and can damage your health, so use with caution.
Yes. There is multiple other options, and also a thorough, comprehensive diagnosis might show very easy to correct causes of this problem.