Can you help with medical diets?

Hi guys, I was recommended this forum as I have to follow a medical diet and I am struggling with my energy levels. I have 2 medical conditions both of which require me to follow strict diets, I also have 3 jobs, 2 of which are quite active as well as having an active lifestyle in general.
My medical conditions are IBS and glucose intolerance, there fore I have to eat a diet that is low in sugar but also low in fibre. I am a cleaner, a companion to a lady with Alzheimers and also I work part time on one yard and I will potentially be starting another part time yard job. In my spare time I ride my own horse and walk my dog (a very excitable sheepdog!).

Currently my diet is:

7-8 am a cup of tea (redbush) and a glass of Complan - I struggle to eat first thing in the morning as it makes me feel nauseous.
10-11 am a bowl of muesli with agavae nectar or honey/toast with jam and a cup of normal tea with one sugar
1-2 pm a sandwich - usually ham or cheese salad, on white bread with a yoghurt/banana/bag of crisps. If I don't have a sandwich I normally have Ryvita with ham or cheese and chutney. I usually have either a pint of ribena, pint of water with this.
3-4 pm biscuits and another cup of normal tea.
7-8 pm pasta sauce with loads of veg and mince/stir fry/jacket potato with a glass of water or ribena
9-10 pm yoghurt and a cup of redbush tea.

Generally I feel that my IBS is under control with this diet but I am finding that at about 3 pm I am knackered! I think it's the glucose intolerance side of things that needs addressing as I feel like my sugar levels are up and down rather than level. My cleaning job means that I do a fair bit of driving throughout the day and I'm not sure if this has anything to do with it?

I would be really grateful if anyone has any ideas as to any changes I can make. As I am so busy during the day ideally I need things that can be made quickly and easily :)

Evie x