Welcome to the forum. Doctors do not have answers unless by some miracle you find one that believes the world is FULL of parisites.
I suggest you start reading on here by searching for your symptoms of hard stomach, etc. It sounds like you are extremely blocked by parisites. The stuff you took helped temporarily because it knocked down the parisites for a bit. It takes long term dedicated work to get rid of the buggers.
Easy things to start helping are take 1 tsp baking soda 2 x per day to change your internal ph. Be sure to have frequent bowl movements, I aim for 3 a day. Stop feeding the buggers by eating vegetables, citrus fruit, and meat and good fat like coconut oil. Coq10 shortage in your body has been shown to allow parisites to live 60% longer than normal, and an increase in Coq10 shortens the lifespan of parisites. Click on my name to see the ParaMed scientific study.