Inspiration and motivation, why is it hard to keep?

The only real answer is to try to better yourself. Convince yourself that you’re motivated enough to do what you want to do.

I’m the same way, and found that when I’m really tired, my mind seems to wander a lot faster thus getting a lot more done. I’m not saying stay up for a couple days to be more productive, but perhaps keeping a notepad next to your bed and sit there writing down random thoughts that come to mind to continue after you’ve had some sleep. Perhaps this will give you a good idea to keep yourself motivated.
Don’t scrap ideas at the drop of a hat, either. Keep them and expand on them the next time you go to bed, if you haven’t done so while well rested.

I would think keeping a journal would be ideal for you. That way you would be able to write down all of your thoughts, emotions, ideas, etc. when you are inspired and have that or read over when you cycle back down into your careless and lazy zone. Then you can keep track also of what leads up to losing your inspiration, what you feel and think that makes it hard for you to keep it up. I would write and draw, write down your dreams, everything. You’ll get to know yourself rally well and can learn to keep focused that way. Or, at least, how to refocus when you become careless sometimes, which happens, as you say, to everyone sometimes.

Because it’s so easy to get dicouraged and/or distracted!

Everyone has those moments. It’s normal. That’s part of life. Now what I’d recommend you to do is take a break off of what you’re doing and do something that you like. For example, when I am at that stage i do several things, i dance, i keep a journal, and i listen to music. When you feel your tired or you concentration’s gone haywire stop what you are doing and take your mind off everything. DON’T THINK. Close your eyes, breath deeply and then open them and you’ll feel much better. meditate. Or take a nap or go to sleep earlier and wake up in the morning first by stretching. Doing anything physical has been proven to help keep those neurons of ours in good health. It distracts and help each neuron mature, which evidently helps us concentrate and redefine our motivation when need be. don’t overkill yourself by staying up late studying several days in a row that will just kill you and you motivation. you need distraction. you are the best person to know what can you do in order to get distracted and have a feeling of accomplishment as well which will also influence your motivation. think about positive things. look forward, and don’t look back on the negative things.
good luck with everything!!!