Why can't I reach the notes I could 5 days ago when I sing?

I love to sing but I recently went away somewhere for 9 days where I didn't have any time or place to sing full out. When I got home, I spent about an hour singing and playing my guitar and I was amazed on how good I was sounding and how many notes I could reach. However, the next day, my throat was a little sore and when i tried singing i couldn't reach some notes that I know are in my range. Ever since then, I almost have to strain my voice to reach some notes and it feels like I have a lump in my throat when I sing and I always feel like yawning. Did I damage my voice by singing a lot when I got back? Or am I not doing something correctly? I need help because I have some things I have to sing for coming up.