As Neil says P&O will be helpful but give them as much advance notice as possible and mention it again to the Maitre 'd on boarding.
No you are not being a pain.... P & O do cater for specialised diets but they must know when you make a booking what the diet is. To find out more precise detail why not ring them on 0845 3585585. ... Neil.
Dont panic! I had a quad by pass 10 years ago and as long as you feel Ok and keep yourself active and eat in moderation you can eat anything, I do.
My wife has the same problem with what she can eat. Each dinner sitting she was given tomorrows menu for lunch and dinner and could pre-order her selection which was then cooked to the necessary requirements. This happened on both the Aurora and Oriana.
P & O are excellent at dealing with dietary requirements - my husband likes cruising with P & O for that reason - you do need to contact them prior to your cruise and give them details. Each evening my husband is given the menu for the next day so he can chose something suitable or they can provide the dish to suit his needs.
P&O are among the best when it comes to special diets. I am diabetic and allergic to EGGS in any guise and choose to holiday at sea because I never have to worry about the food. All you have to do is confer with the head waiter and he will arrange everything for you. Rest easy and have a good cruise.