Hcg level

Hi, I was wondering if anyone has dealt with getting darker positive tests later in the day rather than the morning? I tested one morning & it was a very faint line. The next morning, I got the same faint line. Later in the afternoon, I got a pretty strong positive. This morning, I went to take another one to see if it got darker but it was lighter than my afternoon test yesterday? Is this normal? Should I be worried?