Answer: The mushrooms are growing from the organic matter in your potting soil. Potting soil is made up of shredded bark, compost, sand, perlite and vermiculite. The shredded bark in the mixture probably had mushroom spores in it. (It comes from the forest.) The mushrooms are getting their food from the decaying bark. They won't hurt your plant and they are not all that uncommon. They will probably grow 4-6" and then mature and spread their spores over the potting soil. If you allow that to happen you'll get lots more mushrooms in the soil. They are not edible so I wouldn't recommend you allow them to grow, Dig them out, roots and all, with a spoon and then place some fresh potting soil in the holes you dig.
Your lily will flower when it is mature enough. They usually bloom in the summertime so just be patient with it.
Good luck with your lily!
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