Your kid faking sick to avoid school is normal and a lot of kids do and have faked being sick to avoid school.
I'm one of those kids who faked being sick when I was also 7 and continued faking sick until around 12 years old.
The reason I always faked being sick is because I plain hated going to school as I was very shy, have social anxiety and was getting bullied and picked on.
So sit down with your kid and have a talk with him nicely about what is going on because something could be going on at school which is making the kid upset about going back to school.
Or the kid just might not want to go to school because he hates it.
Maybe look into home schooling your kid if possible or do remote learning which is happening a lot now.
If your kid does fake being sick make sure you keep him in the house and don't let him out and tell him he has to stay in bed.
Or if he's not that sick he has to go to school if you catch him outside playing again.