I am just starting out with FMA (Pekiti Tirsia), so bear with me if my questions are a bit newbie-ish.
I would like to know if it is common to use different sticks for different parts of training. The other day I saw that my instructor had sticks of different width & weight. I was given a lighter stick to perform the first warmup moves. However, when drilling basic attacks against tires, I used a thicker, heavier stick.
I was practicing a bit this weekend (canīt wait for my seconds class...), using a makeshift wooden stick with weight and width similar top the heavier stick I saw on class the other day. It was quite taxing on the hands and forearms, so I was wondering if perhaps I should use a lighter stick, being a newbie and all.
IMHO, I would have to say
ask your teacher. Only he/she knows the path they have in mind to guide you along. Give it time and do what your instructor asks of you.

There is good and bad to both answers, its all about timing...