What's the best treatment for impacted stool? I feel like theres stool stuck in my rectum.

No other disease? One with constipation needs to be sure there is no other disease causing it. If due to slow movement of food and poop through the gut, then things to try are leafy vegetables, water, prune juice, prunes and similar fruits, fiber with water, Miralax (polyethylene glycol), Senokot or other senna, milk of magnesia, or other laxatives. Impaction needs laxatives, an enema, maybe with a helping hand.