Does anybody know what could be causing these leaves to turn yellow/brown? It only started happening the past 2-3 weeks. I've had the plant for 3 years and no problems till now. I can't tell if it's overwatered or if I'm not watering enough. Any tips would be greatly appreciated!!

Without knowing how you've been watering it's impossible to tell. The symptoms are the same. So......

How often do you check the moisture?
HOW do you check the moisture?
Does the pot drain when you water it?
Does it sit in water after you water it?
How have you been feeding it? This can affect the soil and roots.

All of this info can get you to an answer about what's causing the yellowing.

If I had to guess looking at your set up, it's too dry and it's rootbound. How long has it been in the same pot? It's probably time for a slightly larger one and fresh soil

Thank you for your responses! @Gina1960 @CalPolygardener

I recently repotted it 3-4 months ago into a larger pot. It wasn't root bound at the time, but needed a heavier pot so it wouldn't tip over.

I'm thinking it's not overwatered because I haven't been watering heavily recently, and the soil was dry at the time of posting. So I just gave it a heavy watering and have set up a humidifier since the air has been getting dry and cold.

I also didn't mention that I had been dealing with thrips for over a year, and after a long battle finally gave in to using a systemic insecticide. I applied it a couple weeks ago and the thrips are gone, which is a huge relief. But now I am curious if I applied too much and it's causing burning. Is that a possibility? I followed the directions as closely as possible, but added a little extra after noticing it wasn't working all the way after a week or so. That may have been a mistake. Since making this post a couple more leaves are starting to yellow at the edges

I have never used the systemic insecticides that come in granular form so I really can't speak to that. I use Orthene (acephate) a powder you mix with water and spray on. It's not commonly used by home gardeners anymore because it's an Organophosphate pesticide labeled mainly for commercial use, but I ran a nursery for years and I use it. It can't burn my plants. I know that Neem oil can burn plants, but I don't know about other insecticides

Imidacloprid, the active ingredient in the granules, won't burn either.