Hi,
Prolonged bleeding directly may not affect labia, but using tampons or sanitary pads continuously due to prolonged bleeding can lead to labial inflammation and/or infection. The points that can help you are:
- Please consult your gynecologist once and take tablets to control the bleeding. Anti fibrinolytic drugs can help with it. If needed you can also go for 
hormonal pills with her advice to decrease the bleeding.
- Anti-inflammatory and 
analgesic drugs, sitz bath can help in decreasing the pain, 
erythema and swelling of the labia.
- Changing sanitary pads in every 6 to 8 hours, avoiding any particular brand that is expected to give discomfort can help.
- Using sanitary pads or tampons of different companies alternatively can avoid prolonged exposure to the same material.
- Vaginal washes instead of soap will better maintain the local hygiene.
If the swelling increases or swelling in other parts of the body also develops, better to consult your doctor immediately to rule out any other serious causes like uncommon side effect of 
cerazette, coagulation abnormalities etc.
Hope I have answered your question. Let me know if I can assist you further.
Regards,
Dr. Sree Gouri S. R., OBGYN