Breastfeeding a one year old in our society can be challenging because we often feel that the milestone of 1 year means babies should be able to be independent, no longer need the breast, and that we can now make a transition and start doing more. I've found this milestone is more significant for moms than for babies, though.
Breastmilk is still very important for babies, especially at one year and 18 month milestones, and it really is great that you have continued to nurse your son, as this is the best nutrition. Nursing can also be a source of teaching your child that someone is always there and cares, this is probably what you are experiencing now. Your son may be more active during the day and with that activity, some children look for more comfort -- connection to mom at night.
One of the things that you didn't say is if your baby's sleeping arrangements have changed. I thought that when my daughter turned 1 year that we could change our sleeping arrangements -- she was not happy with that at all. This made her more clingy and she wanted to nurse more for comfort and making sure mom was nearby. .
We often spend lots of time trying to get our children to sleep in their own bed, and give them inanimate objects to "love". While my position may not be popular, it worked for me and I think you need to find something that can work for you, allow you to get rest, and provide your baby with the security he needs.
At about one year, in our home, we call the change from infant to toddler and the resultant clinginess "the porcupine syndrome" because while we love to be close and cuddle the quills of the porcupine mom and baby often poke the other.
You might try some soothing methods, such as starting a bedtime routine -- perhaps a tepid bath (if your baby likes baths), a relaxing massage with some light lavender scent, and then swaddling (if he will tolerate it), and a nursing session. The swaddling allows them to feed secure. If your baby wakes up to nurse, you may be able to gradually substitute the nursing with a patting rocking motion.
It may help too if dad is available if he does some of the above. My husband always enjoyed the cuddling up with a book after a bath with my girls. If your baby likes music, you could also play a video of his favorite music -- we loved Hap Palmer's Baby Songs.
Unfortunately, as moms we are on demand 24 hours, and we don't always know what is going on with our children or what the future holds, so embrace this time of change.
I find with any change, and as moms we experience a lot of them as our children grow, that I need to give it time and me praise for my patience (which is often shorter than I would like) to work through it one small step at a time.
Hope this helps. Enjoy this time, your baby is only at this stage once.