When I was running into similar problems - not specifically light headedness, but an energy wall - after about an hour in the pool, my RD at the time suggested that a common recommendation for pre workout is something that his relatively high in complex carbohydrate, moderate in protein, and low to moderate in fats. Extra protein ahead of time did not do much by my experimenting, but that bit of extra complex carb did - it allowed me to break through that wall. It seems that with the complex carb, you will get that extra bit of insulin lift an hour or two after consumption, so that helps to fill in the energy gap you get at that time; at least it worked for me. I also didn't find that I needed it on days that I was only doing weight work, even when that lasted 90 min or so, only on swimming days. YMMV.
For convenience, I ultimately settled on a small meat and cheese sandwich, with a good quality multigrain bread (or toasted.) That may or may not fit with your needs at two months out (I was about four months out when I was playing with this.) IIRC, my now RD nephew used to use some of the original CLIF bars that had a similar profile for this, so that may be something to look into. But that rough macro profile seemed to be the main trick - more fat or protein didn't do much for me, but the complex carb did (and I was never agonizingly low carb to begin with.) Calorically, it was mostly just a reshuffling of what I was already consuming, just rescheduled.
Your plan at this time is somewhat limiting, but maybe some high fiber fruit - berries or the like - as the complex carb may do it, Talk to your RD, as you may get some adjustments to your allowance to accommodate your needs - this would not be unusual for those who are more active than average, as the plans are written with the averages in mind.
Good luck, and have fun, but also don't overdo it - it's easy to do, particularly with trainers!