2 year old speech is this normal?

I am first time mum so this is all new to me, I was just wondering what others opinions as to if this is normal behaviour or not.So bit of back story my son has just turned 2, whilst pregnant there were some issues with his weight and blood flow and I was induced and he was born just over 5 weeks early he spent about 2 weeks in the NICU because of his birth weight of 4.4 pounds. He hit all his milestones within normal time for his corrected age until he was about 12-15 months then he started to slow down a little. He has still got there in his own time but definitely a bit delayed. He is definitely behind in his speech and has just started speech therapy (have only just been able to get him in due to crazy wait times at the moment in my area). I Also believe he may have some sensory issues which we are trying to get him into occupational therapy and a paediatrician which again I am struggling to get him in anywhere public or privately due to the wait times.In the last 2 months (so from about age 22 months) he has shown HUGE improvement with his language he is still very behind he only has about 15 words where he should be about 50 words.Now I am not a singer and probably should have been singing more songs/nursery rhymes to him then I have been but in the last week he has picked up about 3 - 4 words from me singing to him this is a massive achievement for us (he seems to love the song Wheels on the bus so I make up random songs to that tune and he seems really into it and picking up the words)I do/have had concerns in regards to autism but now thinking it could be more sensory issues but not ruling out autism either.Is this normal for a 2 year old or toddler who is in the early stages of learning to talk to pick up words from songs rather then me talking to him?Thanks! via /r/Parenting https://ift.tt/3825N1G