First of all : Miracle-Mineral-Supplement works - I can confirm from several cases in my family. Do not let anybody discourage you. However Miracle-Mineral-Supplement needs to be taken very carefully and you would be well advised to consult someone in your local area with some medical experience and knowledge about Miracle-Mineral-Supplement who can guide you. MMS cannot help you with everything that you may want to cure and you should find out whether it is appropriate for you. And then you should give it some time - especially for those diseases where you can hardly get any other cure you should not expect MMS to make it vanish in a week - it could take a few months.
The symptoms you describe may well be pathogen die-off related or simply your body's reactions in inflammatory tissues. But without knowing more about your physical condition and medical history it is very difficult to speculate on what is going on.
I.e. how is your general heart condition ? Have you had it checked recently ? Since pain in the left shoulder could be a big red alert for some serious heart problems.
A very typical reaction on MMS is, as with many other alternative treatments, that at first the symptoms get worse, sometimes much worse, before they finally get better and eventually disappear. In many cases people feel very weak after a few days of taking MMS, some even get fever.
This is believed to be a result of the body struggling with killed pathogens and the organs being flooded with toxic cell debris and released heavy metals ((http://en.wikipedia.org/wiki/Herx). But also this is due to the body reacting directly to CLO2. Depending on how serious these reactions are you should seek advice from a medical practitioner who has experience with MMS.
Some general advice :
It is a good idea to raise your water intake way above your usual level when taking MMS. It could also be a good idea to combine MMS with NAC/ACC (N-acetylcysteine). MMS seems to be reducing the glutathione level http://en.wikipedia.org/wiki/Glutathione)
and also in some people causes dry up effects to their mucosa. NAC/ACC provides help for these effects. NAC is also believed to bind and chelate mercury, even though this is controversially discussed.
It should be taken 2 hours apart from MMS. Another good way for any beginning is to alternate days on which you take MMS and days on which you take Vitamins and NAC.
Some also believe, that it is a very good idea to drink a few glasses of ozonated water a short while after taking MMS. It is argued that ozonated water could help with further oxidation of cell debris from killed pathogens and thus relieve your organs from those. I personally have doubts about the oxidation of cell debris theory and ozonated water may as well intensify the die-off effects, since ozone by itself is a very strong oxidizer. On the other hand I can see a benefit from additional oxygen brought into the bloodstream which certainly would support any cure.
And finally, what are your doses ? Have you heard that according to experiences made with MMS in recent years it is now generally advised to take smaller doses, but more frequently ?