Ok, that's tricky. I would say it really depends on exactly what sort of symptoms you have. It's an illness that can vary so hugely in severity. My own opinion is (disclaimer - I am not medically qualified, though very experienced as an endo sufferer) if your symptoms are mild, it's probably ok to wait. Ideally you should be seen more quickly, but that isn't always possible on the NHS and being seen quickly might not fit in with your plans right now anyway.
However, if you have any of the following symptoms, get seen as quickly as possible: rectal pain during your period, difficulty passing stools or urine during your period, repeated UTIs or severe bowel problems, or any history of these. These can indicate extensive bowel/rectal or urinary tract involvement. Going privately might be good, but it's worth trying to find out someting about who's the best specialist in your area. Some gynaecologists don't know much about endo - it can be a hugely complex illness with far-reaching consequences for the sufferer, and in some cases requires a high level of surgical skill to to sort it. If you are a complex case, you may also need to be seen by a colorectal surgeon, urologist or gastroenterologist.
Statistically, though, most people don't have extensive bowel/urinary tract involvement, so you don't need to worry too much (unless your symptoms began when you were very young, i.e. under 15, which increases the risk). If you don't have any of the more worrying symptoms, only you know how badly your symptoms are affecting your day-to-day life and how long you can put up with waiting. You could wait until after your honeymoon and get seen then. The only (slight) risk is, that nobody really knows what you actually have until they've had a look via laparoscopy. For example, if you have ovarian involvement you are at increased risk for cysts. If you are ever in acute pain you should be seen urgently, as it could indicate a ruptured or an about-to-rupture cyst.
(I don't know much about waiting times on the NHS, btw, as I lived abroad when I became very ill and so the most complex parts of my treatment were done on the continent. When I moved back here, there was only really follow-up to be done by the gynaecologist. For my ongoing problems I am seen by the colorectal and gastroenterology people rather than gynaecology, and I think it took about 10 weeks to get my first appointment.)
Whether the pill would help you depends very much on how severe it is. Severe cases don't tend to be helped by taking the pill, but I believe mild/moderate cases can be controlled quite well by it. There are several different brands that can be used, so it might be worth seeing if there's another brand that's better suited to you. I can understand that you don't want to gain weight unnecessarily! If it makes you feel bad, then it's probably not worth it. (what's the dress like, btw?)
Another option that was offered to me is the mirena coil. I've been told this can help control it. Maybe it might be an option for you? I refused it myself, as I don't think it would be right for me for various reasons, but might try it in the future if my current treatment lets me down. (My current treatment is the natural progesterone cream sold here which has worked well for me in the past).
I hope this helps, and doesn't put the fear of God into you like the BUPA lady. Please, don't worry too much - I know it's hard, but until you know you have reason to worry, it's better to assume that you'll be one of the milder cases, iyswim. Even if not, it's not the end of the world - there are lots of people who are going through this themselves and who will help you through it.
Take care,
Vigilante