What helped me is using a snorkel.
I got into TI swimming in december last year, started swimming in november, not very fit at all and having trouble doing freestyle for more than 2 laps in one go, then I needed to take a breath.
In december I got the ebook and videos from TI and in one of the images or videos I saw Teryy using the snorkel, immediately bought one and now I can keep going much longer.
I got the finis freestyle snorkel and now just focus on swimming technique and keeping my SPL as I swim further and longer.
Apart from the snorkel I noticed I did not breathe out under water, so every time I breathed left or right, I would first push out and quickly breathe in, which did not help either.
Maybe try a snorkel and see how you go!