This is a
very common problem with musicians over time. I'm also new with the Uke, but I've gone through this on guitar many times over the years. It usually happens to me about once or twice a year for a few weeks to sometimes even months at a time.
Some things I've tried to get out of these slumps are:
1. Let go: stop playing for a couple weeks or even more. Find something else to occupy your time that maybe you haven't done before. I tried diving into listening/exploring some music that I haven't heard before, immersing in it a bit or skipping around a bunch of artists. I've also tried reading a bunch of new books. Sometimes either of these will work surprisingly - I'll pick up the guitar after a few weeks off and after a couple hours find some new refreshing things I hadn't thought of before. Sometimes directly influenced from the new stuff I explored during the hiatus, and sometimes just from forgetting about playing for a while.
2. Lessons: I've never been disciplined enough to take regular lessons on anything. But a few times during these ruts, I found taking 1 or 2 lessons from someone new or in a different style can perk up your imagination. I found this especially true if my rut has been longer than normal. A few little tips or techniques can sometime spur on a lot of ideas or new areas to explore.
3. Sludge: sometimes, you just gotta sludge - drag through the hard or boring times and just play. These are the worst times as you see yourself playing the same stuff over and over, but sometimes you just gotta keep going and eventually a strange chord or run will come out and you'll go "WHOA, what was that?"
4. Play with others: This is probably the best I've found to get out of ruts. Go jam with some friends or some new people you've never jammed with before. I have always learned something new and refreshing doing this.
5. Masterbate. A LOT. Just kidding. I dunno if this helps or not, I've never tested it. I just thought I needed 5 tips and ran aground...