Don't fixate on rank, but on progress. If you are improving and you ukemi is getting better, you are advancing regardless of the belt color. Don't worry. Stay the course.
What Derek said. And welcome on Aikiweb! .)
Rank isn't really about your experience in the art of aikido... it's about your experience in a particular group. You can almost always expect to have to start from zero again if you change dojo, or at the very least, it will take a long time to get to test for the first test at a new dojo.
I changed dojo when I was fourth kyu, and though I was allowed to keep my rank, I had to wait longer than usual to test for third kyu. Our dojo has quite a few students with previous experience, and they all have had to go through this. It ensures that everybody knows what our syllabus is like and is on the same page about the basics.
One thing you can be sure of - anybody with a little bit of experience themselves will know exactly how much you know once they've trained with you a couple times, regardless of what rank you are. So if you do your best to train sincerely, that will show. If you don't, that will show too, however high your rank might be.