I've had one for years. Yes it does feel very painful at first - I couldn't believe how much it hurt , after seeing the little demonstration in the doctor's surgery.
Be very careful to only eat / drink exactly as recommended. If your doc didn't give you a list of instructions ( I hope he did !) there are plenty on the internet.
I'd recommend joining an online Gastic Band group so you can talk to other people with them - it's a unique experience, and none of your family or friends will have a clue about what you are experiencing !
I remember that the most amazing thing about the band, was realising that it does indeed do what was promised - you absolutely won't be able to overeat. Tiny amounts of food will totally fill you up - that took me ages to get used to. In fact I still put more than needed on my plate, because the actual amount I can eat is so small, it still seems ridiculous.
You'll have to get used to explaining to people why you can't eat what they want to serve you. in some ways this is the hardest thing. People just don't understand - they'll tell you "but this isn't fattening - just try some - It's healthy - I'm insulted ". I got to the stage where I just said "I've had surgery - I can't eat much even though I'm sure your food is delicious ". I still say that in restaurants so I don't have to give long explanations !
You'll gradually get used to what you can and can't eat. Some things are a "no no" forever . I still can't eat any red meat, or seafood like lobster - the meat is just too dense and I can't digest it at all. White bread ditto. You'll find your "no no" foods as time goes on. You need to come to terms with these restrictions - as long as you have the band you'll be saying "no" to foods which are essentially healthy, but you just can't eat them.
The main thing you have to practice is "chew chew chew" , chew every tiny mouthful until it's like a liquid. Otherwise you'll get "stuck" as we say. "Stuck" is when you swallow a lump of something - the food hits the band and can't get through so it just sits there and you get a pretty nasty indigestion-type pain . There are ways to deal with it - sipping hot water is fairly effective for me, or a simple trip to the bathroom and a quick vomit . Yes I know, TMI but that's what you do. Then you go back to "chew chew chew".
Best wishes with it - it was very effective for me. I lost a huge amount and though I'll never be thin, I'm normal size now which is wonderful. Follow the instructions to the letter and you'll be fine.