Firstly, I'm sorry that you're experiencing discomfort, but it sounds like you've got good attitude and the willpower to keep trying new things until you find a solution, which is great - the solution is out there, you just haven't found it yet, so it's a case of keeping trying.
Could it be that the stomach bloating and IBS is the source of the appetite problems? I can think of two areas of possible improvement, you're diet and exercise.
Exercise - you say your six feet and 140 pounds which is very thin, this could affect your core posture and put pressure on the internal organs that handle digestion. I would give yoga a try, there are loads of video lessons on YouTube to follow along with and you don't really need any equipment to try it, look for beginner or foundation lessons, make sure to do it every day and stick at it for a few weeks - you will notice after a while your body rebalancing and digestive transit will be improved as well as other benefits - it's legit.
Diet - could you try addressing your gut biome, the balance of flora etc. Try excluding dairy products, especially milk, allow yourself yogurt or cheese in small amounts. Try fermented foods like kimchi. Cut out wheat or glutens. Don't try to many dietary changes all together, be methodical with your inclusions and exclusions so you can log whether there have been improvements.
Also as someone else mentioned, buy a tub of 100% whey protein and have a shake every day. They are extremely lightweight, just a scoop of powder and 100ml of water stirred well. You may find you are protein deficient and muscles and energy starts pouring out of you in huge quantities just from that one small change.
Please give those things a try and see what happens, it may not help you - a thing that works for one persons biology might not work for another, but keep experimenting and it's guaranteed that at some point you'll find the combination of diet and exercise that works for you.
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