It's not rotten milk, that would make you very sick and result in vomitting not unlike food poisoning. It is cultured milk using kefir grains and is similar to yogurt except it contains waaaaay more probiotics in it than any yogurt ever will. It is very common in Russia and is gaining popularity here in the US. Check the dairy section at the market next time your there and you will see a few bottles of premade blueberry and strawberry kefir. It's a drink so it should be near the milk. I make my own at home using grains I purchased online, you can culture them forever. Anyway after a few days of drinking it, the good flora that colonizes in your gut from it will break down your stool and make going to the bathroom easier than it's ever been. People have been drinking this stuff for centuries.
not pooping for a prolonged period sounds like it could be a problem read the label on the laxitives, they may have some warning on them like "if you take these and still don't poop, consult a physician" not pooping after taking a laxitive sounds like a medical issue.
Make some Top Ramen. Spread Country Crock (fake butter) on 6 slices of store brand wheat bread and dip it in the top ramen sauce. Eat all the soggy bread and noodles. If you're not running to the toilet the next day, I'd say definitely see a doctor!