Sorry your evenings are stressful atm. He's at a rough age for sleep as there's a lot going on. Yes, the 4 month regression could definitely be a factor, growth spurt is likely if he's always hungry, and there is a wonder week that starts around 15 weeks and peaks at 17 weeks. Some babies are more affected by these things than others (my second is one whose sleep is thrown off by every little thing so I understand your frustration).
I think pp gave you some good advice, especially not to worry about your LOs needs being met. Your are giving him the opportunity to sleep and helping him as much as you can, but you can't force him to sleep. He'll figure it out and your evenings won't always be this way even though it might feel like it. I do understand the worry about him not getting enough sleep when you know he needs it, but he will be ok, and you need to not stress and feel guilty when things don't go quite right. There's so much changing and growing going on in the first year, please don't drive yourself crazy thinking it's you doing something wrong. These little people like to mix things up and confuse us!
The only thing I can think routine-wise is how does the end of the day look? You mentioned the am nap is good and the pm map is decent with a resettle, but what happens after that? At this age I'm guessing there's still a CN? How does that last nap and A to bed look?
