I used to feel fatigue and even more after eating, felt like I wanted to sleep all day... I now know it was because my blood glucose was hitting 12mmol/l at times. It was a uphill battle but I won the fight.. I had to force myself to exercise.. I could not even do 5 press-ups this time last year, or run or walk 50meters, now I'm doing 100 press-ups/ and squats without thinking about it and running miles. It takes time, lots of dedication, and will power,(and pain for me due to EB) put the end results are well worth it, as I lost 40kg 4-5 months(and kept it off...well it's 46kg now I wanted a six pack
), and now eat normal but healthily food ...well.. I do sometimes put my body to the test out of interest like over Christmas, but thankfully it still amazingly keeps within the 5s, and when I exercise these days it struggles to get above 4s like tonight 4.2mmol/l 2 hours after eating a 70g carb meal. Exercise seems to supercharge the body for many hours after eating. Start slow, even if it's walking to the shops..it all counts. Then build slowly over the weeks and months.
I believe all things are possible, never give up!