A.S.
I am in the same boat - my son is 4 1/2 and the most strong willed child. It's hard a single mother, to MAKE your child respect you. You must be firm and consistent. What has worked the best for me:
#1 stick his nose in the corner (humiliation works for mine)
#2 after school - it's eat, bathe and strait to bed (6:30pm ish) he HATES that, but it reminds him he MUST cooperate or he is punished. (this worked well for a bad day at school - I only had to do that once, and he has been SO much better ever since)
Hope this may help a little...
A.