I always feel bored with everything i do, have felt like this for a while. i know it's not depression as i've had it before so what could it be?

Dysthymia: There are different degrees of depression. These lack of enjoyment is a chronic mild form of it.

Many possibilities: 'Bored' can mean different things, eg, fed up, tired, dejected, discouraged. You list weakness and headache as problems also. Suggest you see your pcp to rule out physical causes for fatigue/weakness. Include meds you take, any alcohol/drug/tobacco use and current stresses. If all is ok, consider seeing a mental health professional to help figure out what's going on that you're bored. See: http://www.health24.com/Mental-Health/News/The-root-cause-of-boredom-20130210