1. Manytimes in online availability it doesn't show that seats are available in SS quota, however when you go on the reservation window, seats may be available. ( I am a bit unsure about this)
2. Reservation forms have been modified now. They ask for whether the passenger is above 45yrs/Pregnant. So that you can be preferentially allotted a LB.
3. For booking ticket in pregnancy quota Doctors prescription and a copy of sonography report would do, no separate medical certificate is required. You also need to carry these reports while travelling.