I have passed the exact same thing on several occassions. It started a few years ago with Tylenol Allergy Sinus Capsules. I took those on occassion for sinus headaches and then one day...not within the next few days, they started coming out, and not without pain. Needless to say I stopped taking those and capsules also. I also took them to the doctor, but I did recieve confirmation as to what they were. It has been a few years, and I recently was put on seizure medication and oddly enough, just last night I had the same attack...and these are pills... with a very thin coating. What you are looking at is absolutely some pill that you are ingesting. Be it a vitamin or medication. My concern, which the doctor explained was...1) how many are you passing and in what time period. 2) are they getting hung up somewhere in the digestive tract, which could be dangerous if something were to cause a bunch of them to break open at once and release the medication or even excessive doses of vitamins at once.