Lemons are very good for you. Natural Vitamin C. Often advised to squeeze the juice of a fresh lemon into a mug and add hot (not boiling) water, use a small amount of Agave Nectar if you really feel the need to sweeten the taste a bit. Take this on an empty stomach first thing in the morning. Supposed to be very cleansing. Do not worry about carbs with fresh lemon juice and it can be used instead of vinegar in salad dressings if you have a problem with vinegar. Lemon and lime juice the enzymes can act like a cooking liquid with some foods - mainly fish, however do not try this unless you have read something about it, for safety's sake.
The pith won't do you any harm and the peel with its wonderful essential oil is also good for you. Personally, I would avoid eating the pips but that is just personal choice.
Just a couple of extra points, if you are referring to whole pickled lemons my initial advice does not stand as I have no knowledge of what they use to pickle them.
Gaviscon is very full of salt so please take care not to use it too often.