The problems you are describing as pain on the left side of your stomach can be because of many reason. Endometriosis
can the one of the important cause. Depending upon the pain description that you have more pain during the period, it shows that the chances of endometriosis is there and it need to be taken care.
Now depending upon the severity of pain and duration of this problem and other investigation you can be prescribed some hormonal
medications which can help to control this endometriosis and can regress this condition. Most of the time medication is sufficient to treat the condition, but some time other intervention may be required. In the mean time you also have to work up with the USG finding of cyst
which may be the cause of the pain and after proper examination and investigation only something can be decided.
The other problem of your oral cavity can be because of the problem which is because of the decaying tooth. I would suggest you to have consultation with your dentist
at the earliest so that other complication associated with decaying tooth can be prevented and in the meantime try to maintain proper oral hygiene
Hope this will help you. Thanks