Why do I get another nightmare everytime I sleep lately?

No More Nightmares. Dreams with unusual content are not uncommon after disturbing or stressful events. Dreams that wake you, flash backs, intrusive memories and recurring dreams or recurring theme dreams are symptoms of unresolved distress. See the No More Nightmares book and a qualified trauma or sleep disorders expert.
Nobody knows. But there are many nice sleep medications that can fix your problem. See a sleep specialist.