17 month old - Ferber Sleep Training help

I did the Ferber sleep training at 6 months old. He did great. However, shortly after he started having back to back ear infections for 7 months. Got into the habit of rocking my son to sleep. Now, he is 17 months old and overall is a good sleeper. Might wake up once a night and need rocked back to sleep. I want to try and sleep train again to get him to fall asleep on his own. Tried to night. I was in the 3 minute cry and he throws up from getting so worked up! It broke my heart so I gave up and rocked him back to sleep. Help! Any advice? Do I try again tomorrow night?