I'm a bloke, not a father but as a childcarer I work with several families whose children are on the autistic spectrum.
Nothing has changed... your son is still your son. He is the same now as he was before you were told that autism is suspected. Don't treat him differently, just keep doing all the things you were before.
Children often have fads, for example many boys like trains. Children on the autistic spectrum may lock on to a particular thing and stick with it for many years. Use whatever fads your son has, to encourage him to interact with you. Spend time down at his level (ie lay on the floor). Take him out to places he would like to visit - if trains are the current fad, then there are lots of places to visit - you will be a steam railway buff in no time!
Aim to spend time with your son at regular times during the week - for example, you could opt for always reading his bedtime story. Try to come up with a routine that suits you and your son.
Try to spend quality time with your partner. Try to find a reliable babysitter, so you can go out say once a month as a couple, without worrying about your son. Have a family outing a couple of times a month, even if it is just to the local park.
Join your local NAS group and borrow books from the branch library - some books on the subject can be rather expensive. By reading more about children on the autistic spectrum you may discover ideas, on how to help you and your son interact.
All children are individuals. Try to accept that he sees the world differently. He may not talk now but he might in the future, so keep talking to him. I've worked with children who at age 3 didn't speak, but come age 5 they did. Alas have also worked with children who by age 9 only said a few words... but they can use a computer and have learnt to type.
Not sure if that is of any help at all, reading it back to myself. Bit hard for me to write about this as I'm not a parent myself... but as a childcarer I accept every child for who they are - they are all individuals.