Well, it's been messed about quite a bit what with the taking out after two weeks of settling to have stones put in (unnecessary btw).

The mix sounds rather moisture retentive and you could well be over watering. What does the mix actually feel like an inch or two down? I'd cut back the watering and leave it alone for a couple of weeks in a shady place. I'd also cut off the flowering stems as it needs all its energy for getting its roots established. I'd also stop feeding it so often. You are making it push growth it isn't ready for. It looks lanky and sad.

Thank you I will try that! Is there a specific way I should cut my plant?

No. Just snip the flowering stem off above a pair of leaves.

You are coddling your lavender way too much! They HATE that! Lavender love...full sun (all day), dry and well-trained soils, alkaline soils,
LOW fertility soils. Your soil is probably too rich and moisture retentive. They love heat, but HATE high humidity and/or excessive rain. They actually prefer a degree of benign neglect. Sounds counterintuitive but it's true. Think Mediterranean, and sun-drenched, arid summers.

I would concur completely with njoasis except that I wouldn't put an ailing plant that has just been transplanted into full sun yet, even one which loves sun when established. And wilting, despite appearances, is a symptom of too much water as well as too little.

I agree with floral here.