Hi supersquish, I have LS and hope I can give you some useful advice.
First of all - steroid creams (eumovate, trimovate, dermovate) are the standard treatment of choice for LS; you are not being fobbed off, a consultant probably wouldn't prescribe anything different. You may have to use it for a long time to see results, and as LS is a relapsing and remitting condition, you might feel it is doing nothing, but don't stop using it. However, some consultants won't prescribe steroidal creams in pregnancy because there is a small risk of cleft palate (opinions differ on this, and the risk in any event is strongest in the 1st trimester).
Secondly, LS can be quite difficult to diagnose and it is quite rare in women of childbearing age (most cases develop after the menopause or in young girls). I was undiagnosed for 12 years. Because of the way LS manifests itself in the skin, a biopsy doesn't always confirm LS even if you have it. Have you had a vulval biopsy before? Personally, I wouldn't be going back for second!
Thirdly, for LS you need to see a consultant gynaecologist or a dermatologist who specialises in vulval disease rather than an obstetrician. They should be able to assess you and write a letter supporting you if a c-section is indicated. I had a c-section on account of my LS and it was no trouble to get the obstetric consultant to agree once I had my gynaecologist (two gynaecologists actually) say one was necessary.
Here is a link to the British Society for the Study of Vulval Diseases vulval clinics in the UK. You should ask for a referral to one of these. If you want to go privately and are in London, I can recommend Professor Wendy Reid or Miss Deborah Boyle if you want to see a gynaecologist. Dr Fiona Lewis is a vulval dermatologist who is also very highly regarded.
Do not scratch!