If you wake up, get up, don't lay about drifting in and out of sleep. That way you may be a bit tired but this will just help you when you go to bed at the end of the day. It's perfectly possible to get too much sleep which will makes you feel lethargic and sleepy as you've been describing. At the moment you're spending about 10 hours in bed..that's quite a lot!
Once you're up then eat some sort of light breakfast whether you are hungry or not. If you're not working at the moment or if you have a lot of free time then get some good solid exercise for a few hours, this always helps me feel better if my immune system is a bit down. It will also make it easier to go to bed earlier and get into a pattern of sleep which is a bit easier to regulate and will make you feel less sluggish.
I'd say the problem is from total lack of routine. You don't eat at set times so your body doesn't know when to expect an energy boost. You sleep when you fancy it and from the sounds of it you might be doing fairly little during the day. Eat regularly & exercise regularly that way you'll go to bed a bit earlier, makes yourself get up between say 9 and 10 so you're not just napping the day away. The exercise will help with feeling depressed to by producing endorphins, your body's natural pick me up.