Hello and welcome,
The discomfort while opening mouth too widely may be due to-TMJ
Please take the Hifenac-MR prescribed by your dentist
This is a non-steroidal anti-inflammatory drug
which is a musle relaxant derivative of diclofenac
So there is no side effect of this drug when taken along with anti-tubercular drug.
I would suggest you to avoid mouth opening too widely.
Mild physiotherapic exercises can be practiced.
Hope this helps.