Working out conception

Hi :-) Bit of a long one sorry . So basically my last period was 25th march , I had spotting 23rd April just light bleeding , i had sore boobs and felt exhausted so I done a test 2 nd may which was faint but positive and since then I’ve done so many tests all positive although darker they are still faint I’m trying to work out conception date can anyone help pls I’d be due on again around 20th this month . I’m just confused as to why They aren’t getting darker , I’ve got sore boobs , bloating , constantly peeing aswell I’m just unsure why they aren’t dark