I just bought my plant last month, and recently the leaves have been getting brown spots on them and the leaves and stems are weak and drooping close to the ground. I kept it in the same pot I bought it in and it had drainage holes. I water it when the top is dry. It gets light from my window reflecting off my mirror. I don’t know what I’m doing wrong.
If it's still in the pot you bought it in, you very likely need to pot it on into something larger by now. I can't see the size of pot clearly in the photo, but it does look as if the ratio of topgrowth is far greater than the size of pot. These plants prefer dappled sunlight or partial shade - direct sun is not appreciated. Hard to say what the brown areas are - exposure to hot sun might do it, physical damage possibly, but check the backs of leaves to make sure there are no insects beneath. The plant is otherwise healthy,evidenced by new growth.
As for its drooping, this plant needs some kind of support to grow up because its a climber- many people use moss sticks so the aerial roots can be inserted into it as they grow, or provide a trellis for it. Further info here https://www.gardenista.com/posts/gardening-101-monstera-deliciosa-tropical-plant-guide/