If your DS is on solids and has eaten a good meal before bedtime, than I think your DS is waking out of habit. My DS is almost 20 mo old and at 18 mo, I decided to try to extend the nursing at night because I was confident that he was not waking up hungry and didn't need the calories (and we both needed better quality sleep). I had already day weaned him at about 16-17 mo.
So, the first time he woke up crying, I just cuddled him and patted his back, and he went back to sleep usually within 5 min. He was frustrated at first that I wouldn't nurse him, but I was surprised at how quickly he got over it. As the days went by, I could comfort him back to sleep in a couple of minutes. I kept extending the nursings by 30 min or so to the point where he was going 10-11 hours without nursing after maybe 2-3 weeks. He still sometimes wakes up once or twice (he doesn't try to nurse anymore), and I always cuddle him back to sleep. Now, I think he is waking because of dreaming, temperature, etc. Still trying to figure out how to keep my little blanket kicker offer warm.
I am down to just nursing him to sleep at night (having cut out nursing to sleep for his nap a month ago) and I plan on weaning him next week when he is officially 20 mo old.
I was pleasantly surprised at how easy the whole process was, having anticipated the worst and thinking I would be up with a crying toddler for hours at night. That didn't happen thankfully.
Best of luck to you.