Yawning is a common occurrence when doing breathwork. The prana that the breath brings in results in the impulse to yawn, but lessens as you build up your energy reserves. Beyond this, I have not heard of burping / yawning ongoing in conjunction with EC work, although it is always possible. As clearing starts, it affects the physical body, and any kind of reaction can occur. Always observe common sense, and pull back on the EC work if any physical symptoms seem extreme.