[mdjlucan]

Lavender The lavender stem where the flower comes out what is causing it to go very thin and die

[New shoot]

That could be a couple of things.

They have dried out and wilted at some point.  The tops of the flower stems have gone too far and have not recovered.

They have been battered by weather - strong wind, hail, torrential rain - and the tops of the stems have been damaged and are now dying off.

Either way all you can do now is trim back those damaged stems.  If it is all over the plant, cut them all off and hopefully you will get another lot of flowers before the summer is out.  A liquid feed would do the plant some good - general purpose feed, tomato feed, whatever you have.