Missed period

I’m 10 days late for my period, my cycle happens usually every 29 days .. last month I was my period like the 6th so usually I was suppose to start like maybe the 4th or 5th of this month.. I never have this problem which is why im kinda concern.. Im not ruling it out to be pregnant so soon.. but what else could it be? I know periods are very different sometimes but this isn’t a regular problem for me, it’s actually the first time it’s happened.. I just took a pregnancy test and it came back invalid! I’m just trying to figure out other possibilities before I start thinking about pregnancy! I know it’s a real possibility but I haven’t had any symptoms and I feel if I was, the pregnancy test would’ve came back positive.