I'm not a doctor so I can't really help you on that part, but I am seventeen and I can totally understand how you're feeling. I don't think I have IBS but I have been having digestive problems over the last few months and I think we can all agree, digestive problems of any kind, are a complete nightmare!
I don't know if I've got some underlying problem or am just unlucky enough to catch every stomach bug going. I do know that I've got to apply for university in two months and have to do some stuff over the summer, but I can't do any of it at the moment because of my stupid stomach. I too have had diarrhea first thing in the morning for the last week, right up until dinner time, so I can't leave the house until then. I can't do any of the stuff I need to do because 12/1 pm is too late and I'm worried I'll end up having diarrhea the whole day. At this rate I'm going to be in bed all summer, too afraid to leave the house, and I don't fancy telling the professors of the very competitive university course I'm applying for that I didn't do anything over summer because I had diarrhea!
I really do feel your pain and every doctor keeps telling me that I just have a stomach bug every time. Maybe I just keep getting a stomach bug every month, but it's still really distressing and annoying. I had something pretty similar to what you described last December. I was due on my period and woke up in the middle of the night with this awful stomach pain and my stomach was making these horrible sounds. I had the worst diarrhea I've had in my life all that night, all that next day and all that next night. I was severely dehydrated, could barely walk and ended up losing a stone. My mum used to be a nurse and has seen everything, and even she was shocked at the state I was in. I went to the doctors and they just told me I had a stomach bug!
Then all of a sudden the stomach pain and diarrhea stopped and my period started straight away. It lead me to believe that it was PMS as I do get that really bad, but that's no excuse for losing a stone in two days. I used to suffer with extremely painful period pains and the pain was so much more painful than the time I fractured both my shins. I think it was wrong for that doctor to say you just have painful periods. I can tell the difference between period pain and stomach pain and I'm pretty sure that you can to.
Your stomach can become a lot more sensitive when you're on your period because of the hormones, I think we will all experience it at some point, but if you're feeling like that then the doctors need to do more to prevent it. Sometimes people can experience IBS, or IBS like symptoms, at that time of the month so surely there will be some type of medication to help with your symptoms. I'd suggest visiting your general doctor and telling them what's going on. Hospitals can only really give short term solutions, and with diarrhea they can't really do much unfortunately because of complications. General doctors can refer you in the right direction and work on some long-term solutions. I wish you all the best!