Insomnia Support Group
Insomnia is a symptom, rather than a disease, and is characterized by inadequate quantity or quality of sleep. People with insomnia complain of difficulty falling or staying asleep, which results in significant impairment of daytime functioning. Insomnia is categorized as transient (shorter than one week), short-term (one to three weeks) or chronic (longer than three...
First there is a difference between tired and drowsy. Because you say you can sleep well (at times) I presume by tired you mean fatigued, as in physically fatigued.
Sleep apnea can be one cause of this. In other words, people with apnea often tend to feel like they slept but still awaken unrefreshed and feel fatigue during waking hours. Not sure if you've been checked for this or not. It is treatable.
Second, what this really sounds like to me is depression. That would explain the lack of energy and all the negativity you're expressing. Not sure if you've been evaluated for this, but depression is often correlated with sleeping problems as well. Also treatable, and often responds especially well to drug-free cognitive therapy.
As always, trying to get at the true root of your issues is the best way to make it better.