Praise be to Allah.
If this uncertainty come after you have finished doing wudoo’, then do not pay any attention to it. If it happens before you finish, for example, being unsure whether you have wiped over your head and you are washing your feet, then you can wipe over your head and wash your feet. There is no hardship involved in doing that. This is if you are not suffering from a lot of insinuating doubts. If you are faced with a lot of insinuating doubts, then you should not pay any attention to that, and you should proceed from the point at which you are now. So if you are washing your feet then you may assume that you have wiped over your head. The same applies to all other stages of wudoo’.