Sorry for the length and a bit late to the party but I have done/still do the FODMAP diet. I actually was referred to an NHS dietitian, for those who are worried that they haven't been and are missing out I would say that there is limited provision all around so it isn't really the case that some people get a 1-1 on call dietitian to support through it.
The referral generally gets you a place on a group session that lasts approx an hour, (with an optional 1 hour follow up session a month later) you are given a booklet advising foods to avoid/foods to limit/and foods you can have, and the nutritionist ultimately went through the booklet page by page with us and answered any questions for the confused at the end. She was lovely, the booklet is a great reference point but nothing groundbreaking or that isnt available on a quick google, in fact ( very rudely) a lot of people left mid way through when they realised this was all it was, and didn't put their name down for the follow up).
I tend to just buy foods when i shop from the 'allowed foods' list to make life easier, with a couple of bits from the 'you can have some of this' list, such as hard cheese, some berries etc. You may find it helpful to make a note of the amounts - the booklet we got says for eg " hard cheeses- 1/2 a cup'.
The biggest tip I can offer really is check ingredients, things you stick in in general in cooking are secret offenders, stock is not Fodmap suitable ( though you can buy some online, i will dig out the website if you need). Also Soy sauce- opt for the gluten free "Tamari" type if possible, and if you miss garlic, you can use garlic oil instead to cook with (though if i use too much i get stomach ache).
The nutritionist was pretty lukewarm about kefir/probiotics but suggested they are worth a try, as was ingestible aloe vera. She basically said that if you are going to do nothing else, cut out onions, garlic and tomatoes out entirely ( including the stocks/gravies/crisp flavourings/onion powders in foods) as these are the worst offenders. Also opt for lactose free soft cheese or milk if possible if you think lactose is a trigger for you.
Buscopan isn't too bad for stomach cramps, steer away from ibuprofen for the pain as it can damage the stomach lining. If you have acid reflux or upper GI symptoms persist with your GP and ask for medication, omeprazole i have found helps, or if you are after a non medicated option, consider "silicolgel" - i've tried it recently and so far really feel its helped.
Feel free to PM if you like, i'm fresh out of 3 years endless referrals for gastric issues so have been around the block!