okay I will see if I can help, as it sounds like you have a few different things to figure out.
Are you doing pat/shh or pu/pd, if your lo is 3mths old then try only pat/shh. What I did with dd is I would pat/shh her until her eyes were starting to roll, and she was pretty out of it, that way she didn't have too much work to do by herself, but it wasn't done completely for her, IYKWIM.
Try to leave the room if he is sleeping, it may help him to self soothe a little easier if you leave him to it.
Are you able to figure out if he is actually crying or mantra crying? it may help you to figure out if he is simply settling himself or if he needs you.
Do you have a copy of BW solves all your problems, if you don't have it I highly recommend getting it, it has become my life line in trying to figure out what to do.
On the nummy thing, I take it is a soother, I have done both, my ds had one till 18mths, and dd has only used her fingers. It is a personal choice if he is able to settle without it then great, but if he needs it then it may get tricky once he looses it in his sleep. KWIM.
For now that is all I can think of, stick with it hunny, keep me/us posted if you need any other ideas and let us know how things are going.]
Good luck.