Is it necessary to enter the bathroom before every prayer to check for the intermittent yellow discharge, or is it sufficient to estimate its presence, and is it obligatory to perform ablution for every prayer?

You are not required to search to verify the discharge of secretions; rather, it is sufficient for you to rely on the original presumption, which is that nothing has exited. If you see them, then istinjāʾ (cleansing) and wuḍūʾ (ablution) become obligatory for prayer. If you doubt the time of their exit, attribute it to the latest possible time they could have exited. You are not considered mustahāḍah (one experiencing prolonged non-menstrual bleeding) as long as the discharge is minimal, unless you do not find sufficient time to pray with a valid purification. Your wuḍūʾ is not nullified by the entry of the time for the next prayer, and you may pray with your previous wuḍūʾ as long as you have not verified the discharge of secretions.