Welcome to citrus
It really cant be grown as a houseplant for too long, usually just to overwinter them. If it cant go outside its life will be short lived.

the rocks at the bottom wont help drainage as eventually the soil will fill the gaps aiding in the pot holding water. Regular potting soil is a death sentence for potted trees because of compaction and holding water too long. There are many post about great soil mixes that will allow the trees roots to not drown and get enough water and oxygen to grow very healthy.

the fert spikes shouldnt be use either and using a liquid fert is much better. Miracle Grow all purpose is a good one but doesnt have the trace elements that citrus need. Foliage Pro can be found online and contains all the nutrients that citrus and many other plants require.

the pot may be too big holding too much water and not allowing the roots to dry out. Citrus hate wet feet and need to dry out between waterings. With the right soil mix you could still use it just fine.

I know it sounds like im scolding you but these are the lesson most of use have learned and Im just passing them on.

good luck

Hi, I bought my first citrus tree (Meyers lemon)two years ago and did exactly what you did and what the majority of people do. I immediately got a larger pot and lots of new soil. I think I bought the Miracle grow cactus and citrus mix which is suppose to be the worst stuff you can get. It was purchased in the fall because I saw it on sale for like $24.95 and it was a large bush shaped tree. It was like a 5 gal container. I put it in the south facing window and watered regularly. It had lemons on it when I bought it. After those lemons matured as the winter went on the leaves started to drop until there weren't any. I put it outside in spring and it didn't do anything. After reading up on it here, I pulled it out of it's container to find that it hadn't grown new roots at all. The exact same root mass. I put it back into the original trade pot and lightened up the little bit of new soil I added with perlite and bark so it drained well. I read here that the best advice was to just leave it alone. That summer I had nothing but flowers that dropped overnight but it eventually recovered and did great over this winter in the house. Look up Turface too and see if you can get some. Its what they use in the athletic fields to help drainage. Somewhere in this forum is a formula for mixing good citrus soil too. I find they love liquid nitrogen and keep a look out for scale. If you find the leaves sticky with sap that is scale excretions or poop I guess you could call it. I used all season dormancy oil for that.
Good luck

"the rocks at the bottom wont help drainage as eventually the soil will fill the gaps aiding in the pot holding water"

Yes this is true. If you want to use stones for drainage they must be toped by fine stone then sand to stop the soil from filling in the rock.

Wait untill the soil is dry befor watering. Keep the ph low.