I take calcium, magnesium, hair/nails/skin vitamin, iron, and fish oil vitamin. how am i supposed to feel and how to i know they are working?

Hard to know: If you have had a deficiency of one of these vitamins or minerals, your symptoms should gradually improve- hair/nails will take a while because of slow growth. If taking for general health, it is certainly tricky to know because the goal is to not develop a condition. So, if you don't develop a condition, is it because the supplement helped or if you wouldn't have got it anyway. Good luck!