Okay there are a few things going on here that should be rectified asap. The Flukers orange cubes are probably the worst gutloads on the market. Stop using them. 2 commercial gutloads that are good are Repashy Bug Burger and Cricket crack. I'd get my hands on one of those as well as supplementing your commercial gutloads with fresh fruits and veggies. sandrachameleon has a wonderful blog on here that goes far in depth of what you should be feeding your feeders. I suggest you check that out for more information.
Your supplements are way off. Jacksons can overdose really easily on supplements so you have to be really careful with what your dosing and how often. Calcium WITHOUT D3 should be given a few times a week, and calcium WITH D3 maybe once or twice a MONTH at the most should be given to jacksons. Also, a multivitamin should be given once or twice a month . DO NOT give calcium WITH D3 that often. This could potentially be the cause of the hunger strike or the runny BMs, among many other things that could go wrong in the future if you continue this supplement schedule.
Jacksons need high humidity, so 40-60% on average is not high enough. I'd look at the range of 60-90%, 60% being the lowest, and 90% spikes throughout the day (after misting). Is he in a glass enclosure or screen? Jacksons should be in a screen cage for optimal airflow, but screencages have a harder time holding the humidity. In that case, tarping off 3 sides should help retain it. I would consider purchasing a misting system to help keep the humidity up. Mistking is a great product, and it really does help if you're not home to mist 3-5x daily. Fill your enclosure with live plants as they also help retain proper moisture levels. I would also maybe consider purchasing a larger terrarium for him. Jacksons love to roam, and need a lot of space. I'd go with a 2'x2'x4" enclosure for optimal room for him. Reptibreeze has a great one, that is relatively inexpensive compared to glass enclosures.
This is a lot of information, I know. But it should help your situation. Take it one step at a time, but I would really start with upping your humidity levels at all costs, as well as fixing your supplement schedule asap. Then work on proper gutloading and then move onto a larger enclosure. Hope this helps!
Christine