@Blueberries0112
I would have him tested for it. The sooner , the better for him
You can't really assess an 18 month old for autism with much reliability (in the UK).
However I would be asking for a referral into your preschool camhs as they can help begin assessments and help you with the bond between you, I wonder if VIG (video interactive guidance) would help.
For now, try a technique based on attunement. When ds is playing calmly, just sit nearby and begin mirroring him. If he picks up a brick and sucks it, you do the same. If he throws a car, you do the same. You aren't trying to engage him, or seeking eye contact, just copying. Then if/when he notices he may begin doing more things to see if you copy and thus can lead to shared enjoyment. You can also begin extending the actions, eg he picks up a car, you pick up a car, he puts his to his mouth, you do this briefly too then put it down and go 'brrmmm' while rolling it along (not making him watch). He may then begin to imitate you which is the beginnings of attunement, turntaking and trust.
You can also choose one particular rhyme eg round and round the garden and when he is calm and sleepy begin by singing it, not to him with eye contact but just in the room, them nearer, then do round and round on teddy's hand, your own hand, then ask him if he wants to do round and round on mummy's hand, daddy's hand etc and then eventually if he would like a turn and then you can do it on his hand.
What I think you may have is a highly sensitive boy for whatever reason, and he senses your stress and anxiety that your thoughts about him are inducing. There is no way that he hated you as a newborn, and those worries and hormones have maybe minutely affected the way you feel in terms of how relaxed or competent you are, and it's a vicious circle. That's why these low pressure mirroring and attuning activities - where you place very little expectation upon him, and "strike" while he is busy, happy and relaxed, might be useful to try. It may take weeks and weeks to get a breakthrough so don't be disheartened if nothing changes quickly. Know this: you cannot harm your child by sitting near him and playing alongside in a gentle way - so the very worst outcome is nothing. But I think you'll get results. He is still very young.