Op, if you are worried I would say speak to a professional atleast just to put your mind at rest. As speech is the main thing then possibly an slt would be a good one to start. Have a look if you have a speech n lang drop in at local children's centre, or if there are any dates where slts come to stay and plays, then you can speak to them in an informal setting and they get a look at your ds while he is playing and see how he interacts with them. If they have concerns they can then refer him on just from that initial meeting, or they may be able to reassure you.
I would also say pop over to the sn section here if you think it would help, even though your ds may not have autism or any sn but it is something on your mind and there are loads of very knowledgeable and helpful people over there - getting more info can not do any harm, so worth bearing in mind.
Also do get the hearing checked even if you are sure that he doesn't have hearing problems, some dc are so good at coping with the hearing loss that you will not know they have it!! Hearing loss does not mean they are completely deaf, it can be to different levels so sometimes they can hear but not clearly. Think of when you put head under water, you can hear but very muffled, so would still be able to respond sometimes and follow instructions but it would make everything more difficult, especially if you are trying to learn to talk and still building up the vocabularly. so it is a definite one to check and that's the first thing to do normally.
My ds2 does have autism (he had/slightly still has some hearing loss too, so its not necessarily just one or the other) I first wondered about this from him being about 18 months, he was diagnosed a couple of months back, at about 2.10
My ds is also very affectionate, sociable and all of that. He is actually more sociable than my other 2 dc and people always love him the most cos he will go to anyone. In his case it is actually part of his autism, he doesnt quite have the normal social boundaries, he doesnt have the normal wariness of strangers that other dc may have. He also has a very good memory, so if theres anyone he's met previously even once or twice and they were nice to him he will remember them and run straight to them and hug them, he is very loyal like that! However cos of his personality, at first when I started to wonder about autism, friends and family would all be like nooo, of course not he can't be autistic he is so affectionate! It is a myth though that children with asd can not be affectionate.
With your ds, because I am quite a believer in mums instinct, i would get him seen, and keep records of what he can, can't do and anything you think may be relevant, just in case you do end up needing it. If these concerns are what you genuinely feel then don't have to listen to your mum or others, she may be a teacher but doesn't mean she is automatically right.
In my case, my ds has an uncle who is actually a paediatrician! (not developmental though i think he does other stuff) and a good friend who works in children's centre so she is qualified in early years stuff and used to see my son every day - they both at the start were among the ones telling me no, he cant be autistic, dont be silly etc etc. Because people care about your child (like your mum) they may well be more reluctant to consider that there could be a problem. because they dont want there to be. if that makes any sense??
Early intervention is important and the longer you wait before getting him seen initially, the longer before he would get an assessment - and the waiting times can be very very long, so the fact you've noticed some concerns now is a good thing IF (and he still might not!) he has asd, then the sooner you could get him some help. Sounds like you are doing a lot to encourage him anyway, playing and talking is the main thing whatever the situation. Whether he does or doesnt have asd just keep doing that as much as possible. Do you know all the usual slt techniques of using shorter simple sentences, speak slowly, comment on what they are doing rather than asking too many questions - etc etc, as all this will help either way.
Good luck and I am sorry for the massive post!!