You are not alone. Just last summer I had about 2 months of vacation, and except for the Lite Challenge, I did nothing concerning art or cartography, I spent the whole vacation thinking on what could my tale (for some sort of challenge a publishing house was running) be about, also I wanted to draw some maps for any future campaings, or just to improve skills. Guess what I did? Nothing, when there were two days of vacation left I got the idea to draw Arcantis (which, btw, is still not done ), my tale I got a good idea by the mid of march (after 15 days since vacation finished), but the deadline was on april 11, and I couldn't get it done in time.
Sometimes I sit down to think, "Well, now what could I possibly write/draw about?", and then when I check the clock "five minutes later" , Oh my! I've been sitting for an hour now, and my work is pretty much nothing. It does is only when I have the time knife behind my back that I start to really get the ideas and work, though not always I have enough time to finish them.