First off-it's very hard but be patient and give it time. I have been there and my daughter is not almost 14 months and I think I am seeing the night more and more. It will get better.
I second the recommendation on adding cereal to the baby food; do not put it in his bottle. I did the adding cereal to the food to make sure she is full. I nursed until 10.5 months and found that once I stopped nursing she stopped getting up every hour-she obviously was not getting enough to fill her tummy at a feeding.
Others advised of the overtired syndrome as well. That is true from my experience. One school she was in was not laying her down in her crib during the day for her naps so she was waking before she was well rested-only getting 2 short 30 min naps and then maybe passing out exhausted for an hour after 5 when we got her home. I changed schools for additional reasons but she was lied down in her bed as requested at the new school. She immediately was getting 2-1 hour (minimum) naps during the day. She might power snooze for 30 minutes in the evening but that was ok. I consistently tried to make sure no matter how much she slept during the day that she always was in bed by 8pm. We have to leave by 7am. Anyway her waking decreased to 2-3 times once the longer naps during the day were introduced.
Gas drops and teething tablets. Another cause of my daughter night waking at your sons age and even now is acute gas pains and teething-can make it difficult for her to fall asleep. I use the teething tablets sold in the pharmacy section of Target-just as the pharmacist. They are homopathetic so they contain no drugs and are dissolvable-my daughter loves them cause she knows they will make her feel better. 2 is all it takes after I brush her gums before a bottle when I know they are bothering her at night. I use mylicon gas drops for her belly.
Just give her water at night. I still give my daughter Formula at 14 months before sleep times and when she wakes in the morning, just to make sure she is full and getting enough vitamins. Since about 11 months I assured myself of her nutrition in take during the day and took the advise of just giving her water after she was lied down at 8pm. I started out by watering bottles down ~2 months prior until we got to just water. She now knows she will not get milk/formula until after 5 am at least. This is the time acceptable for my husband and I to wake. You could decide on your own wake-up time.
I feel for you and am scared of having another child because I feel like I haven't slept in 2 years-couldn't during the pregnancy either. My daughter did sleep 10 hrs straight the last 2 nights. Yeah! Your son will do this also just be patient and try to enjoy the mommy time and comfort of knowing you are taking care of his needs and being there for him. Obviously, I don't believe in the CIO option.
A book that also helped was the no cry sleep solutions book that was recommended to me by moms on this site. It was a very quick read-I know just the thought of reading a book almost made me pass out of exhaustion and that's why it took me several months to break down and order it online. But I read it on my commute and ~2 days.
Good luck and stay strong-you'll get to sleep some day.