1- Yeah, a lot of people don't have nightmares that they remember. I haven't remembered one in several years...
2- Yes, stress has a MAJOR effect on dreams. There's a few ways to get rid of stress, but I'm no expert on them. Just google 'stress relief techniques'.
3- Dream Journals are a major help. Just write down anything you remember-even if it's just a color or a smell. After a while your recall will improve.
4- ...