Will massetters be affected when talking so long? My jaw felt tired/fatigued. I don't want them to get big

When the masseter muscles are fully treated with Botox, they will be relaxed and unable to contract and become larger even with eating, speaking, chewing etc.  You can track the amount activity in your masseter muscle by feeling the sides of your jaw.  During the 3-4 months that Botox is active, you should not be able to feel much of a bulge.  When you start to feel the movement of the muscle again, it's a good time to retreat the area.  

There should be no issue with doing regular activities after botox injections into masseter muscles.

Thank you for your questions. This should not affect your Botox results, or affect the size of your masseter muscles. It does not apply much force across your muscles, as occurs with eating.  Botox also helps shrink the masseter muscles by preventing them from squeezing, similar to when a person stops working out and their muscles shrink.  Hope this helps!