Designing tests that need to be changed often is a sign of high coupling between your tests and your solution, which in turn is often a sign of brittle design. You are testing an implementation and not a ndesired feature. Another potential problem is that your interfaces are changing too much, which means you are having trouble with thinking it out.

Possible solutions to this are TDD, or trying to write your tests in such a way that they would fit any implementation of your interface. For interface design, outside-in TDD is an interesting tool.

In any way, your problems with tests at early stages probably come from lack of practice. Doing less tests is certainly not going to help.