why won't he propose

We've been together over 6 years. Own a house and have just had a baby. The midwife was makin comments as to why we're not married and that there's no excuses to not have a ring and it's made me feel very insecure. He always says in a few years to people but it's right what the midwife has said, if he's thinking about getting married then why hasn't he proposed. 
I don't want to be an old bride or be that person that will have to say my boyfriend rather than husband when I'm much older. 
What's your advice girls and boys.