Ugh, sorry about the cheating ex. That stinks. So, hormone imbalance can cause that type of brown spotting. Example is if you make too much progesterone. That is probably separate from the new symptom of itchy vagina and swelling. When you see the doctor, don't lump them together. And hopefully they do some lab work on you to check your hormone levels. Are you on the pill or anything?
The itching and swelling may be a yeast infection. Those itch Your doctor will swab your discharge and be able to tell you. You can take a pill the doctor prescribes or use an over the counter product like monostat one day ovules.
When is your doctors appointment?