H.W.
I have an 18 week old girl and she has been alot fussier lately, being a bit more difficult when it comes to bedtime. I think my baby's problem is her teeth. She has no teeth buds yet, but is fanging everything during the day, and hardly having daytime naps, so she's overtired when it comes to bedtime. And then sometimes, she just won't settle down unless she's lying in my bed being breastfed. It's the one thing that I know will always put her to sleep.
This is just a friendly suggestion, because I know I do the same thing. If that was the first night it happened, don't stress too much, unless it happens for the next 2 or 3 nights.
He might have just been a bit upset and needed his Mum nearby.
Whenever something changes dramatically with my daughter, I tend to flip out a bit, but more often that not, it doesn't keep happening (whatever it was).
My baby is mostly breastfed and we have a loose routine. I can tell when she's ready for bed and we'll 'usually' shower, then feed, then either rock her to sleep (if she needs) or just pop her in her bed and give her back her dummy if she needs it.
I would suggest starting a sleep routine, if that is what is best for you. If you are happy with the way things are at the moment, then that's fine. Do what works for you.