Achy lower back pain lead to pregnancy

So my period is 9 days late, I would be 5 weeks along. I have gotten like 4 negative tests but last week was dealing with nausea, I’m tired I could be sitting or standing all day and when I lay down I have lower back aches, hell idk what’s wrong with me? Anybody have any similar things happen and get positive tests 10-20 says late?? My period has been pretty consistent since August of 18 and all the sudden I’m just missing one?? So confused 🤦🏻‍♀️