Oh dear, the first time I read the title of your thread, I thought it said: Why do fragrances turn me on? He he he, says a lot about my mind...
I think you can rule out the idea that your body chemistry somehow causes all fragrnaces to turn bad on your skin. What you are describing sounds to me more like changing preferences and possibly a sensitivity to certain chemicals.
Do you tend to wear one fragrance day-in day-out, or do you mix things up on a regular basis?
Do you have a tendency to apply fragrances quite heavily?
Have you tried any niche perfumes? (As a general rule, I find they often have a less 'synthetic' feel to them than designer scents).
I'm wondering if these factors may be implicated in your woe.
Wearing perfume should be a joyous, uplifting, positive experience, so I really hope you get to the bottom of the problem.
Probably others can offer a better response.