I'm still confused

So I started testing pretty much after AF left on the 12th of February. For a while I was getting negatives. A few times I got very faint lines which I know are negative but then would get no lines after for a while. Then I got a positive Monday the 26th at night and the next morning

I had sex Friday and Sunday before I got the positive.

Is it normal to get faint lines and then no lines at all before getting a full positive?? And what are my chances at becoming from those two days?