I would think that the reactions that you are having are more from 'different' strains rather than pesticides. Just because a dispensary says its White Widow or Gorilla Glue #4 does not mean that it is actually WW or GG #4. There is no standard for potency, nor for testing genetics. Anyone can pretty much call any strains whatever they want, really. Also even if you grow the same strains under different conditions, the resulting cannabinoid and terpene levels will be different, and the high will be different.
It can also be issues with 'organic' pesticides used. Just because someone grows organic does not mean there will not be any pesticide residue. There is a large list of legal organic pesticides, including Neem oil, Aza (Azadirachtarin), and pyrethrins in particular. You could be sensitive to any of those, and they are considered safe and organic, and generally are not tested for (though pyrethrins have been found in some lots tested by labs in Oregon weed in high amounts, and the lots were flagged by the labs and had to be used in making oil which strips any pesticide residue). You could be sensitive to any number of organic (or inorganic) pesticides. You could also be sensitive to soap or oil sprays. There are many of those out there as well, and they are mostly organic.
Now in California the pesticide regulations are stricter than pretty much anywhere else. Or they will be shortly. Here in Oregon every harvested lot of weed has to be tested for pesticides before it can be sold. So its all pretty safe here. All of this said, many pesticide dissipate rather rapidly. Abamectin for example (sold as Avid) is a strong miticide and pesticide and it is certainly not organic (though it is derived from organic sources, so I have issues with its classification), but it will dissipate within 45 days time. It will dissipate faster (usually in a matter of days) in UV light. I know many people that have sprayed with Avid early on and had it tested after 45 days and it passed lab tests with 0 residue of abamectin. Aza will also dissipate rather rapidly, especially in UV light. So again, how its grown can make a huge difference in the results.