Positive fades to negative

I️ have taken 4 tests over the last 5 days. All 3/4 of them have came up positive with a faint line that’s clearly visible, but disappeared. The first test was FRER, second was EPT and these last two were Walgreens brand. I’m not too familiar with pg tests, do they fade? Or am I️ pregnant? Af due in 3 days I’ve just been feeling off so I️ thought I’d take one. Once I️ got the faint line I️ couldn’t stop and now I’m all confused. 🙃 is this common for tests to do?