Could I still be pregnant?

Okay, my period is 3 days late which has never happened to me before. I’ve been off birth control for 3 months. I tested the day my period was due and got a negative, I waited 2 more days and tested again yesterday and still negative but no period. I am confused as to why I’m getting negative tests but my period is late. The first test I took was FMU and the second one was in the afternoon. I am on a diuretic so I’m wondering if my urine is diluted making it hard to pick up hcg levels?

Edit: thank you to the few of you who responded!! I am now 5 days late for my period and according to the app, I am 19 dpo. I do not track ovulation other than what the app tells me. I got another negative yesterday morning. The last 2 days I have had slight nausea in the morning and before bed. I have 2 other kids and I got positive tests pretty early on with them so I don’t know what to think :(