O.D.
My first daughter used to do this, but when she was 3-4 years old. Now she is 7 and she plays with her 4 year old sister. She still wants from time to time to play with me, but since she goes to school full day, when she comes home she barely has time to play with her sister. It may be that your son gets bored after he comes from school and he wants someone to play with him. It can also be that he wants attention. I am sure you have your hands full with three kids, especially the baby so he may want more attention. My older one used to throw tantrums when her sister was a baby (things like,,why do I hold her in my arms,etc).
Since he is almost 6, you can give him assignments. There are all kinds of books with activities for his age (math, tracing, writting). I don't know if he reads or not..if he does, he can read a story. At least this would give you some time to do other things in the house.
good luck