My son is exactly the same age, and I have found that he is so sensitive to small changes in our relationship.
I'm a little distracted and extra tired at the moment and his behaviour has taken a major backslide.
I've also heard of a fair few toddlers having delayed reactions to a new sibling.
and if he's getting molars on top of all that I think that makes for a pretty reasonable explanation!

I'm trying to build in as much connectedness and play as I can. He was whinging last night after a rough bathtime and it took all my strength but I pushed all my frustration to the side and said "hmm, it sounds like you need 20 kisses!!" and once he'd giggled through those he said "more kisses!" and it did make bedtime a little easier.

There are lots of suggestions for creative connection etc on Laura Markham's website. I think she is just fantastic.
All the best, its so tough and I imagine a whole lot tougher with a 10-week old!