Re: nystatin and triamcinolone safe on foreskin rips?
Nystatin is an anti-fungal (anti-yeast). Your doctor must have thought it looked like a yeast infection was present. And that's not at all unlikely. Yeast infections are also something that can cause foreskin tightening. (If tightening happens suddenly & unexpectedly, that's a common cause; though when it persists from infancy as is more common, the tightness wasn't originally caused by yeast, but they could definitely be contributing to problems stretching now.) Yeast infections are not uncommon when foreskin issues prevent better washing (esp. after puberty). I would be careful to keep any globs of Nystatin from getting in any tears until they heal, but you definitely want to use it at least around the area. It should help a lot.
Triamcinolone is a corticosteroid to reduce inflammation/irritation from the infection. It is also recommended to keep it out of torn skin, though doctors are supposed to know when to ignore such recommendations. Still I would definitely be very careful to keep more than the tiniest bit possible from getting in the tears. And I wouldn't use it any longer than necessary to heal, because long term it will make the skin thinner, which can make it tear more easily. You might increase the risk of future tearing by using a steroid cream for too long.
There are also some really powerful helpful dietary things you can do too. You will want to avoid all the dietary contributors to yeast problems in order to overcome the yeast as quickly as possible. Milk and beer are the worst. Most other dairy is bad too. Yeast extract is in a lot of food and bad. Most other fermented foods and drinks are bad too. Most vitamins, minerals & other supplements are bad for yeast. (Vitamins in healthy food are still good of course, just no pills.) Avoiding sugar helps too (especially fructose, glucose). Kind of bizarrely, cinnamon actually often helps a bit. (But don't ever consume more than normal/small amounts; larger amounts can cause muscle tremors that resemble Parkinson's disease--temporarily.) You will find you are much less susceptible to yeast infection with these dietary changes. For more yeast-avoidance food & other advice Google: candida diet
Another dietary consideration, calcium makes stretching more difficult. Lowering dietary calcium intake can help stretching--especially if calcium intake was high/too high. Hard water has a lot of calcium (if that's what you have in your area). Watch out for "calcium fortified" things and of course dairy until you're done stretching. It should make it a lot easier. (Calcium also does a lot of necessary things like make muscles strong, keep us from getting fat, and keep the immune system active, so don't drop your calcium as low as you can for a prolonged time, just lower it if it's high.)