Hi There!
First of all, congrats to you for trying so hard and having a cute little baby!
I'm sure you are doing wonderfully!
Have you tried the wake to sleep method?
If you know he's hard to settle after 45 min, try to go in there very calmly at around 40 min into his nap, gently stroke him or pop the paci back in, and he may transition softly into the next sleep cycle.
My 9 week old also wakes up regularly after 45 - 50 min. Sometime I get him to settle again, sometimes not. Usually I go in once, give him the paci, tell him that I'm there and that everything is fine and that he should try to settle himself ( I literally talk to him like this: "Hey sweety, try to go back to sleep okay? If you need help, just call me, I have the baby phone with me. Good night sweety"

. Then I go out and leave him to it.
7 out of 10 times he will need around 20 min of fussying (he's not actually crying, more like moaning) before going back to sleep, and 3 times, he doesn't manage and gets upset, so I get him up.
Don't stress too much about it.
Gently try to keep him awake a bit longer every time, he may get more tired.
Just be calm and remember that neither you nor him are failing if he only sleeps 45 min each.
Maybe he's just happy to see you again after 45min!
