Advice needed!

I am 4 weeks 3 days pregnant with my second baby (have a 21 month old son) but I think I'm freaking myself out! I took a FRER test with SMU on Saturday morning (4+1) and it was a faint positive, so I took another test Sunday with FMU thinking it would be a darker line but it was pretty much exactly the same as Saturday's 😕 took another test today at lunchtime (only a 2 hour hold) with a different brand of test and it was quite faint. Should I be concerned? I feel worried as I'm sure at this point with my son my lines were quite dark. I haven't had any bleeding, I'm tired, have on and off cramps and am fairly nauseous but don't really have any other symptoms. Last time my boobs hurt so bad I could barely wear a bra but this time they just feel normal! Any advice would be great, I think I'm going to drive myself mad haha.