Hey there and Welcome to BellyBelly!
Congratulations on the birth of your son!!

It seems that most babies go through this stage at around this age. I would almost say its normal. I know how frustrating it is too. But I can say it does get better.

Does your son cry when he wakes up? Or does he just stir and make sounds?
I was just googling this for you, and because i was interested to know, and it appears that the reason babies wake usually after one sleep cycle, is because they are in a "Quiet sleep" at this stage of the cycle and are easily woken. Sometimes they dont wake enough to wake up and gain their second wind, but most cases they do. Also another theory is that they wake from thier sleep cycle, and look for Mummy/Daddy/what ever comforts them enough to get them back to sleep.

I wish i could offer a solution, but I cant but i must ask, have you tried patting him to sleep while making soothing SHH sounds? It usually doesnt work instantly for me, its something one needs to persist with, but i do find that does help quite a bit when im desperate enough to be patient enough.

I have learnt that what ever approach you take you should be consistent. Allow yourself a set amount of time to persist with it, so say you set yourself 15 mins of patting your DS, if it doesnt work by then get him up an dhave a play, and when he does show tired signs again, persist again for the same set amount of time. Its up to you how long you will persist for, and what you will persist with, and try keep it the same between yourself and your husband.

Your doing a great job and i hope what i had to say made sence and was helpful to you in some way.
Good luck!