The idea behind minoxidil is to maintain the hair you have. Some hairs are genetically programmed to be shed and cannot be saved. If at all possible, switching to finasteride would be better as is slightly superior to minoxidil. In some instances, minoxidil will cause an initial shedding but that resolves over time.
Your doctors told you the correct answer that minoxidil sometimes induces a shed when it is started but it usually goes away in a couple of months
Usually does not cause hair loss that was not going to happen anyway. Also , in most situations transplanted hair is not affected by minoxidil very much.
Topical minoxidil can (but not always) cause shedding. It doesn't mean it is "working". It is a side effect that may reverse. It is best to follow up with your doctor to make sure the medication is right for you.