Just wondering if this happens? Can Losec stop working?

My poor boy is sooo unhappy these last few days, he has been taking Losec for the last 3 weeks and there was a massive improvement, but things have gone down hill really quickly.

Do i take him back to the GP? I feel like i can't do it anymore. He is arching and squirming, and just crying and crying and crying. I have been so careful about what i am eating, i have cut out all dairy, spicy food, soft drinks, chocolate and caffeine. I feel like giving him formula as i can't help but feel guilty that my milk is giving him so much pain, but i tried some formula a few weeks ago and it made things 100 times worse. He is propped in his cot and i keep him upright 90% of the time, i actually rarely put him down.

Our GP suggested starting solids early, so he has been having rice cereal for the last few weeks and some avocado, pumpkin, carrot and banana. I did give him 2 of those rafferty's packs on wed/thursday (apple, pear and cinnamon and the pumpkin apple and sweetcorn one), could this be causing the problems?