hey carly,
my little boy is 14 months and had no signs of crawling at all. he would get up on all fours but never actually moved no matter how much we encouraged him, we bought him toys, left our phones out for him to get and even bought a carwling winnie the pooh but nothing worked, he still isnt crawling and isnt walking either, he will walk woth us holding his hand but as soon as we try and let go of his hand he just makes himself fall to the ground.
I really wouldnt worry about it, all kids are different and he might just suprise u one day and get up and toddle away, if you are still really concerned then give your hv a call and see what she says.
Sorry i couldnt be more use,
claire xx