I had thrush practically from the moment I weed on the stick with my first pregnancy. I hadn't ever heard about the possible link/misdiagnosis of group b strep but my baby was born incredibly ill and spent some time in NICU (about a week with the first couple of days being very touch and go). I say this not to scare you but to urge you to get that swab, as I say I'd never realised it could have been something else.
In terms of treatment, nothing really worked I'm afraid. I tried to limit sugar as much as possible. The thrush cream was helpful, I applied what felt like gallons of the stuff and as many oessaries as I was allowed (I was advised that it was safer to apply with fingers rather than the applicator in pregnancy although advice may have moved on since then, my pregnancy was 8 years ago). Also of course 100% cotton underwear, loose trousers and if you really feel the need to wear pantyliners (I went without in the end because anything synthetic just made me feel grosser) then definitely unscented or even try cotton reusable ones)
Medication wise, initially I used the 'normal' treatment eg what canasten is made of but my gp tried me on a more old fashioned treatment. I'm really sorry, I can't remember what it was called but it was what they used to treat thrush before canasten became popular, came in pessary form and if I remember correctly the pessary was more like a 'gel' capsule (like a see through gelatine type capsule like nurofen) rather than the chalky canasten pessaries. That was more effective for sure.
The good news is that as soon as I have birth it went away pretty much instantly, honestly it was almost miraculous. It never entirely went away during my pregnancy but the pessary alternative to canasten and the copious amounts of thrush cream did do their best to keep it at bay. It was utterly miserable though so you have my sympathy (and of course now I'm wondering if it was never properly treated because it wasn't actually thrush! This is going to send me down a rabbit hole!)
The good news is my DS was entirely unharmed by his sepsis and NICU stay. No hearing loss, limbs all present and correct, no organ failure etc etc. in the interests of total honesty he is autistic but this is nothing to do with group b strep or sepsis or the like. There is autism and other neurodiversity within the family and autism has a strong genetic link so that's where that comes from! He's a bright little thing, fantastic at reading and concocting stories and non fiction, amazing at working out 'how things work' and has decided he wants to be a DJ or work in music production because he likes working out 'all the different parts' of a song and how they go together 
I'm sure you're not even thinking about a second baby right now but just in case you ever were I didn't have a repeat of this in my second pregnancy. I was really worried I would and it genuinely gave me pause when thinking about ttc but I didn't have a single episode of it.
I don't think thrush in pregnancy can ever be attributed to development issues with the baby, it's usually just because your hormones are going wild and your poor vagina is over compensating. However on the off chance it is group b strep I will urge you once again to get a swab for that (swabs available to purchase online or sometimes from local chemists, I've seen them in mine) as that can be nasty and can lead to issues post birth. You'll need to get one quickly so you have enough time to swab and send it off for testing. Good luck op and I hope your discomfort ends soon!