My mom is going through this right now. Please if it gets bad see your doctor and request a CT of your abdomen. Mom was backed up completely!
Short term: 2 ounces prune juice, 3 tablespoons Cherry milk of magnesia, plus a plunger! (Not joking, you'll be needing it!)
Starting tomorrow: no less than 64 ounces of water, psyllium fiber, avoid constipating food like cheese, add vegetables with fiber. If this isn't enough, get a prescription for lactulose. Even if you have insurance, if you have a tough time getting it, go through goodrx. (Trust me, pharmacy will accept.) It will cost you about $25, BUT over over the initial hurdle, take just twice a week.
Warning: it's STRONG. The first day, try one teaspoon (5 ml, not 15 ml). I can use even less and get results! So ignore directions, and you'll get a lot for your money!
Good luck. And please, if I helped you, I could really use the 10 points!