9 weeks will not nap more than 15-20 minutes

[Melimat]

Unless he's on someone or in the carrier, my 9 week old son will not nap more than 15-20 minutes at a time. After that, he usually startles himslef awake. I've tried sitting next to him and patting him while he transitions into a deeper sleep, but it's as if he never does. He still startles himself and will sometimes calm back down only to repeat again, or he will wake up and I can't get him drowsy again. I've gone through this for over an hour, with him continuously stirring. I've also tried swaddling him but it doesn't help. At first I though he would grow out if it, but at 9 weeks, I'm starting to wonder what's going on.

[Ima shel Alon]

For how long have you tried swaddling him? It can take a while for it to work with a few babies so I would still try it out for a good while. There is no harm in it anyway.

Could you post your day in an EASY format so we can have a look if some of his day needs tweaking? Maybe he is OT or Ut.
But I tell you now already that at this age there is not much to do. Such young babies still need a lot of help falling asleep AND staying asleep.

There are 2 methods here that might help you: How do I address habitual wakings? (wake-to-sleep and other methods) but really only if his EASY is age appropriate.