I think you have to try to be more civil about this. Your parents are your parents, and however weird and disgusting it may be for you to imagine, think let alone hear them have sex, they are adults. They do have a libido, and they regrettably have to get rid of their horniness by having sex, as well as appreciating each other and showing each other how much they are still in love. To a certain extent you should be happy that your parents are still in a loving relationship, but that's not the point here obviously, so I'll move on. I don't see the problem with the lingerie. I've loaded our washing machine before, and my mum loads it sometimes. We both have to touch every family members clothes, and I think you just have to try and ignore the 'ick' factor. Collect the clothes in a big clump so that the lingerie is on the inner area. But even then, it's not like the clothes are encrusted with filth. She did have to wear it, so I doubt it's covered in mud or anything. It's not really any different from your mum touching your underwear. Try and be more adult about and mature. It is just clothing after all, you're hardly touching their skin or private area directly.
About the sex, she probably wants to just keep you safe. She might want you to not have sex for the exact reason she did. She might have realised later on that it was a mistake, and that she regrets doing it. You don't know why she chose to have sex at 21 and you don't know how she felt afterwards, you're just invading her intimate privacy by reading her therapist notes. Those are private and you're not supposed to be reading them. She trusts those around her to not read into it, because they obviously won't get the full picture and could misinterpret whatever is inside it. Choosing whether or not to have sex is a very personal choice, and if you think you don't want to wait until you're married, calmly bring it up with your mum. Ask her why she thinks you should, and explain to her maturely without shouting why you don't want to wait. But don't, under any circumstances, bring up what you found in the notebook. She might get angry or be highly disappointed in you reading it. You could get her to bring it up by saying, "so were you married when you first had sex" or something similar. But keep in mind she might lie to prevent you from getting the wrong idea, or making the same mistake she did. She can't force you not to have sex, but don't get angry at her for what she's trying to tell you. She loves you and wants what's best for you, which in her mind is advising you to not have sex when you're not married. She wants to prevent you from making the same mistake (if it was a mistake) that she did.
Be more grown up. So what if she had sex in that bed? She probably washed the covers and the pillowcases and the bed lining, so I don't really see the problem. She is your mum so I highly doubt she'd let you sleep in the bed where she had sex without actually cleaning any of the linen. Consider it a nice gesture that she's moving floor so that you don't hear them have sex, which might be really awkward and annoying for you.
It's not really nice to think about parents have sex, and it is disgusting to a certain extent. But you have to bear in mind that they are humans with a sex drive, so try to give them their own space and respect what they do. I'm sure they're not trying to annoy you on purpose, and probably try to hide it from you as best as they can because they know it's not something that any child wishes to talk to their parents about.
- Balazs