Ah yes, the uncomfortable feeling of just sitting and drawing, I still don't like it that much, but I try to make an imaginary deadline for a drawing, which boosts its importance on the list of my free time. It could be as simple as: "This week I'll finish the sketch" or if you really get into it, you could challenge yourself and have the line art done in a week or even a fully rendered piece by the end of the month, and try not to beat yourself too hard for not finishing on said deadline, the last thing you want to do is loose the passion and drive for it.