Very very faint second line/evap line

Senel

I've had this happen to me before and again last week. I get very strong pregnancy signs so test and I've tested all week and keep getting this very very faint second line which looks like an evap. I've tried different brands. Some people can see this linw but some can't. I'm now getting a clear bpn on same tests.

Anyone no why I've had this??