Switched from desogen (ethinyl estradiol and desogestrel) to generic apri. are there any differences?

Yes: Generic versions of medications are usually fine, but they are not identical. The fda allows for a modest degree of difference in "bioequivalence". Essentially, a generic medication is allowed to be sold if it is between 80% - 125% of the brand name medication. Most generic medications are fine for most people, but there is always some percentage of patients for whom they are different.