It is so very hard isn't it we went through this about the same age, it all got better, and are now going through it again! It's funny, I always thought night sleeping would be the issue but it's always day sleeps that drive us round the bend. I feel like I recommend this book alot, but have you read the No Cry Sleep Solution? It has great suggestions on different methods to try, but it doesn't give you an overnight answer, more like a framework of solutions that you can choose to apply to your own family/situation.
I don't have any real other advice in the sense that I am having major day sleep problems at the moment with DD, but I do keep telling myself that it's just a stage she's going through and it will improve. She had a pretty big developmental leap around 12wks that I feel threw her out for about a week, with really similar behaviours to your DS. I think/hope we're mid another leap now and it will all calm down soon.
I know what you mean about feeling anxious when nap time approaches, I have been feeling the very same way. Sorry I couldn't be of more help