I am sorry to hear about the difficulties you are having at the moment. The nursery should really have given you some guidance about how to proceed since they made these observations.
What you need to do is take your child to the GP and ask him to refer the child to a child development team. These teams are specialised for autistic children. They would then normally assess the child, speak to you and the nursery and give a diagnosis if this is appropriate. Depending on the child's condition and any difficulties you are dealing with they may offer you some psychology input in order for you to understand the nature of the diagnosis and be better equipped to manage your child' behaviour if it is challenging.
They would be able to offer you any input they feel necessary. The priority for you is to request a referral to the team by your GP.
I hope this helps
All the best