What is the expiation for perjury?
Perjury is forbidden and one of the major sins that require turning to Allah in repentance, seeking His forgiveness, giving back rights to whom they belong, or seeking their forgiveness, and expiating for that oath.
Is it permissible for one to masturbate in order not to commit fornication?
This is called committing the milder of the two evils such as eating a carcass in fear of death, and this happens when committing fornication is very likely to occur.
After a month and a half from the end of postpartum bleeding, my wife occasionally finds a small amount of blood, and she is breastfeeding. What is this blood, and should she fast and pray when she experiences it?
This is postpartum bleeding, so she should not fast or pray until she sees the signs of purity, unless it exceeds sixty days, as the maximum duration for postpartum bleeding is sixty days, and the majority of women experience forty days. If it exceeds sixty days, it is considered irregular bleeding (Istihada). It would be advisable to consult a doctor after the sixty days. And Allah Knows Best.
Is it permissible for a person who has to make up for missed fasts to fast six days of Shawwal (the month directly after Ramadan) before making up for the missed fasts?
Yes, it is permissible for him/her to do so, but it is better that they make up for missed fasts first. And Allah Knows Best.