Hi Jules,
I am also on omeprazole, and a gp recommendation, I take vitamin d and b12 to keep them at an optimum. She gave me no indication these would interfere.
I also am on prescribed iron twice a day, and evening primrose oil. Oh,and flax seed oil, all with her knowledge.
I am careful to separate all my prescribed drugs separately. i.e I take the omeprazole at lunchtime, the collection of vitamins around 5pm
I also have to space out thyroid, and 3 lots of arthritis medication and painkillers! I hope one day to be able to get off some of these in time, but sadly all are necessary right now.