Hi banja, welcome to PsychCentral!

I have low energy at times myself...

Do you have any psychological illness, like depression or anxiety for instance? It can cause lethargy and make you feel tired with the whole low energy!

It could be anemia (low red blood cells) which you can "fix" by eating more protein or supplementing with an iron pill. Actually, if you can find a good multivitamin, it's always useful providing you tell your doctor/pharmacist about any other medical conditions or medication you take. I see you've tried a multivitamin before, but it's worth it talking to your pharmacist again to find another better one - not all are created equal!

Do you take any prescription meds, or anything herbal that might affect it?

Are you sleeping enough, or getting enough (not too much) exercise?

It could also be low blood sugar, which causes me to feel lethargic and dizzy and just generally tired with low energy when I don't watch what I eat.

I'm not a doctor by any means, but perhaps this is something for your doctor to help with ... more than any of us can unfortunately. If not that, see a nutritionist or a counsellor/therapist, and they should be able to help!