baby congested

my son is 5 months old. he’s been congested only at night time for about 2 months already. every single night. i’ve done and tried everything to prevent it and nothing works. so i’ve asked his doctor about it & what she recommended didn’t help & wasn’t really even a good recommendation at all. I took him to another doctor he recommended benadryl. all they’re doing is listening to his breathing nothing else. not doing any other test or anything !!! should i take him back and request something else to be done !?? i don’t know what to do at this point. the doctor i spoke to over the phone said he could have a condition & i forgot the freaking name but nobody else has mentioned it but her !!!