Hi Teresa. I would definitely go for a bigger pot for that plant. I think it needs to be even a little bigger than the clay pot you have it sitting in. Be aware that for indoors, a glazed pot will hold more moisture than an unglazed clay one, as the clay transpires water so will dry out the plant quicker. Going into warm weather, you'll be watering more often anyway, so a glazed pot might be a good idea. Buy a good quality bag of sterilized potting soil to add to the new pot, too.
You do need to get some high quality timed release fertilizer. The home made things like coffee grounds and compost tea will not be enough. That's a pretty big, high demand plant. (especially when it's making lemons . . .
) Here we have specific formulations for citrus that have micro-nutrients. But for your little tree, just a 'complete' fertilizer for indoor plants is probably what you will need to use.
There were probably a few mite eggs on the plant when you got it. If it was grown in a greenhouse until now, and has been in there all winter crowded with other plants, it's very easy to get a few tiny mites hanging around. The greenhouse people most likely have an insect mitigation routine that keeps them under control, but you really can't ever get rid of every bug in a large commercial greenhouse. So when your plant went to the store or nursery where you bought it, then came home with you, those little nasties had no more treatments, and have multiplied. If you see any more speckled or mottled leaves - you can check easily by running your fingers along the undersides of a leaf. If it feels sort of sandy or slightly rough, and your fingers come away stained a little bit yellow, that's the signal the mites are back.You can also sometimes see tiny webs in the leaf axils. A very mild solution of dish soap will kill them off if it gets bad, 1/2tsp. per quart of water sprayed all over and under, then rinsed off in the shower. But just giving the plant a regular shower will often keep the mites away.
