I bet the root of the problem is that you compare yourself to other people too much. Because I have never considered giving up a thing I love and am enjoying *unless other people are in the picture making me feel bad about it*. Like, I have never sat on my bicycle, with the sun shining and the wind blowing flower petals past my face, thinking "my cycling is too slow." Not unless some young guy on a racing bike blew by me. If I'm alone on a road enjoying the day, how can I be too slow? I can only be too slow if there is external pressure for me to be faster, and the external pressure comes from competition or other people's demands.
So I bet that you look at other people's art, you want attention, you don't get as much as some other guy, and then you feel bad and lie around and go "my art sucks". If this sounds familiar, eliminate the other guy from your life as much as you can. Spend your time drawing things you enjoy drawing and skip the part where you make yourself feel shitty about it. If you like *drawing* then draw.
If that's not the problem, then you probably don't like drawing as much as you like the idea of being an artist. If that's the case, then motivation probably won't work and you need to find a hobby you genuinely like doing.
Perhaps you should try some art using new tools. I recently picked up some ink brush pens, fell in love with them and all I wanted to do was keep drawing. I had to adapt the way I worked, I discovered some artistic issues I didn't realise I had, and the pens challenged me to push myself. Choose something new and give it a go. You may just break yourself out of a rut!
If discipline is the issue, there's nothing anyone can say or do instead of you to help you out. This is something you work out on your own by gathering up all the willpower you need and JUST. DRAW.
Identify things that stop you from drawing (for example surfing on deviantART admiring other people's work..) and get rid of it. Log out. Turn off the computer. Leave your phone in another room. Gather all the supplies you need, prepare your work space and just sit down and draw. That's really all you need to do. To sit down and draw.