BFN in morning but nausea in afternoon


I am four days away from my AF. I experience irregular periods. My husband and I are TTC with our first baby. I can’t pinpoint how long my cycles usually are. My last period was August 29 and we BD the whole week of sept 9-14. I’ve been too excited and have taken a pregnancy test pretty much every day during the week of sept 16-21 and all were negative. I took a urine test this morning and it came out negative. But I’ve been nauseous all afternoon. Any advice???