There is a lot of confusion over the topic of Niddah and I want to try and clear some of this up in Leviticus 15.
Verse 19 is Normal bleeding
Verse 25 is Abnormal bleeding (miscarriage, etc)
Verse 28 IS NOT connected to verse 19! Verse 28 is talking about ABNORMAL bleeding.

Verse 31 is WHY being clean is important ONLY if you are going before the altar. Staying in your house with your wife is not a sin while she is on her menstrual period. You don't need to have separate bedrooms and kitchens, etc.