Well you are obviously doing something wrong, perhaps watching some tutorials might give you more insight into the workings of a bicycle.
https://www.youtube.com/results?search_query=replacing+bicycle+bearings
That's what I've tried, maybe I didn't put enough grease inside, but what I remember from putting the bearings in the front is that the hub kind of loosened, then one fell out and the rest came out, I noticed my back wheel was a tiny bit loose but didn't change it at the time, now the hub came loose and the bearings came out, I did actually put the grease on it though, maybe it wasn't thick enough, but I think maybe the rain thins it.