A.P.
I felt like I was reading about my first baby, I understand how frustrating and difficult this is for you. My daughter never took a nap longer than 30-40 mins at a time, I hated trying to get her to sleep because like you we had to rock her every time, she never slept through the night either, she would wake up three times a night, I wanted to rip my hair out.
When I look back (my baby is now 4) I Wish i had known about acid reflux. She spit-up like crazy and only seemed to fall asleep in the sitting up position, because she never feel asleep laying flat. Does your baby spit up a lot? Do you lay your baby on his back? I would have have the baby checked for acid reflux and would start laying the baby on his tummy, see if this helps. I wish I had layed my first on her belly, I did with my second baby at four months and he slept much better for me. I had better luck with "The Baby Whisperer Solves All Your Problems" than I did with her first book, I felt like there was more information. Is it also possible you are missing his tired cues? I know I did when I went back and looked at the video footage, I was overstimulating her on top of allowing her to become overtired, which I didn't realize at the time. Also, some babies just thrive on less sleep if your 100% sure he doesn't have reflux or isn't overstimulated.
I'm telling you what I'd wish I'd done, because I believe now it probably would have helped me, but I struggled with my first for awhile tt