I just bought this Begonia a couple of weeks ago. It was perfect for 2 weeks, then the flowers started turning brown. :-(

At first, I watered it whenever the soil felt really dry. So, I thought, "Ok, I guess I need to water it more." So, I put some coffee grounds on it for good measure, poured water all over it, let the water drain out the bottom, but

the flowers continue to turn brown.

What is wrong? Too much or too little water? I can't figure it out. :-(