Breathlessness and lethargy

Ive had some very complicated IBS issues recently which lots of you may have seen me post about since May but I believe they have calmed down quite a lot thanks to a food diary and very mild medication (imodium) when I really need it. Funny thing is though is that ALL of the other symptoms I used to get (i.e. sometimes nausea, lethargy and headaches) completely vanished when these problems arised, probably cos I cut 80% of my diet out.
I lost around 11 pounds and am now roughly 48kg and 172cm (Im female) and wondering if this is why all of a sudden I feel exhausted, breathless and generally "meh". I must confess since facing the HORRIBLE anxiety over these IBS issues which have dragged on I have made time to walk at least 2 miles everyday as it relaxes me but Im gonna take a wild guess and say my body cant do this anymore as the weight has dropped off me all of a sudden. I dropped down to a scary 44kg back in 2015 and was very nearly on a drip, I basically had a flare of my emetophobia and after seeing my housemate catch a bug I stopped eating more than one meal a day. Also should say since my stomach is a little better Ive gone back onto sugar quite alot (I was a REAL chocoholic having up to 200 grams per day) and Ive become so relaxed this week that Ive had quite the lot of cookies and cakes so maybe thats why I feel crap.
Anyone else feel this ?? Im wondering too if its the sun, we never get it in england and Ive been laying in it up to 3 hours a day sometimes.

Cheers x