It is good to think and good to challenge received wisdom. It is a vital part of growing up and becoming a well balanced, astute adult. Until we find our own truths, we are just living the conditioning other have imposed on us.
The fact we can't see the sense does not mean there is no sense. No one sat down and invented our way of life just to annoy kids. Our way of life evolved over thousands of years because, for all its faults, it works for the vast majority of people who are willing to cooperate in making it work. It might be that we just can't see the sense or that something has changed over the years so it is no longer as sensible or that it is never really was as sensible as others think ... which brings to another point: Just because people say something is so does not make it so.
For example, in your question, you imply life should have a purpose or a point. What is the basis for that belief? You suggest "just about everyone says that having a job is the whole point of life" whereas that has not been my experience. I have never heard anyone say that. They have said you need to work to support yourself and to give you the financial means to enjoy leisure time and old age. That's different. It is certainly not the point of life.
I disagree that sex is unnatural. It is very natural. You say sex is disgusting so I have to disagree with you on that point too. We may well be conditioned into certain attitudes by people with damaged minds or their own agenda but that does not make it true. I agree that marriage is unnatural but it is really just a formalisation of pair bonding which is entirely natural and offers evolutionary advantage.
Reproduction is entirely natural. It is a selfish instinct without which the human race would cease. It is not an instinct I choose to indulge. We do not have to be slaves to our instincts. We can choose. I would never want to impose life on a child, but maybe that means I am 'damaged' in some way. That's OK. We all have choices. I cannot expect to impose my views on others.
I believe you are starting to think in a positive, analytical way but that you have some mental exploration yet to do. As a young person (I am guessing) you do not yet have a wealth of life experiences on which to draw in order to evaluate ideas. That's OK. No one else did at your age either. Please keep questioning but may I suggest being cautious in drawing too many firm conclusions or feeling bound by earlier conclusions. The older I get, the more convinced I am that certainty is probably the luxury of almost complete ignorance. I have been SO certain in my time!