Pest/disease ID help?

Hi all, new in here and to growing peppers in general. Long story short, late last summer I threw some bell pepper seeds in a large container under my deck and kinda forgot about it, came across it with several small plants and admittedly didn't thin them out well or early enough imo, so two are in this container currently. It made a single tangerine size pepper last year and now I have two, but the plant is starting to turn yellow a bit. I have not fertilized at all, it is in a mix of pretty much unknown soil and miracle gro. I have seen some very small spiders but I can't seem to find mites or identify what is happening here. Zone 6 near Kansas city, MO. TIA for any help!!