It's great that you seem to be getting things sorted well and clearly having your MRI on day 12 will give them a good chance to work out what is going on.
I have been on chemo for 16 weeks and have 9 rounds to go then surgery and radiotherapy. My cancer is Invasive ductal carcinoma but the MRI was able to pick up some small DCIS which was not seen on any other imaging. The reason that I have had to undergo chemo is because my tumour was large and had already spread but yours may not be like this so hang in there and be guided by the medical team looking after you. I hope your results are encouraging and you only need minimal intervention. I know that it is the waiting that is often the hardest part but just try to stay busy and get on here for support if you need. Good luck. Pollyrose