1. Warfarin is not known to cause photosensitivity, it is ok for you to be in the sun while on it.
2. For general information, please visit out website at www.drugstore.com, then type gabapentin in the search box.
3. Vitamin D3 is usually taken with calcium to prevent osteoporosis or to treat hypoparathyroidism. The dose will vary depending on the indication you're taking it for.
If you want to know more about your medications, general questions OR specific ones, you should ask the pharmacist where you pick them up. Pharmacists go to 6-8 years of school and intensive training to be able to answer these questions and make sure you take your medications in a safe way.