I gave my dog, 9 years old a bit of cottage cheese with dry food. Since then she is acting strange. Her head is down and it appears that she periodically trembles. Is that a belly ache and what can I do

There's no way to know if the cottage cheese is what's causing this, other than discontinuing the use of it, and seeing if she improves.

It could be a belly ache, it could be something else totally unrelated to the cottage cheese. To be safe, take her to a vet.