I hesitated to respond, as lithodora performs a bit differently here in the NW. Unless planted in very well draining soil and in full sun, lithodora here will experience center dieback in winter, usually due to too much moisture. They are cut back hard now and that typically will generate new growth from the interior (provided no root rot present). Shearing back after the initial bloom flush (as one would do with helianthemums) should result in additional flowering.