Don't worry! Your symptoms are actually pretty common-- but because women rarely discuss things like periods and yeast infections with one another we often have a tendency to freak out over totally normal experiences.

A lot of women experience changes down there following their cycle. The pH level of your lady parts is normally somewhere around 3.5 and 4.5. However, since the pH level of blood is much higher, changes in pH often accompany menstruation as well as the time directly after menstruation. Bacteria tend to thrive in higher pH environments, and as a result many women experience bacterial vaginosis as a result of higher pH levels during and after mestruation. Some women may develop yeast infections after menstruation if the body tries to return to a normal pH level and over-corrects, therefore killing the good, yeast-fighting bacteria that was already present.

These infections are totally normal and the bacterial one tends to clear itself up on its own in healthy women. You should go to the doctor if you are unsure whether you are getting yeast infections or bacterial infections, but once you know which one you are more prone to around your cycle than you can easily deal with them. As I said, BV generally goes away on its own but if the symptoms last longer than you would like or are more invasive or painful than normal, you should see a doctor to get placed on a low-dose antibiotic. For yeast infections, most can be cured by over the counter inserts and creams such as monistat. However, if you happen to have decent insurance, the copay for the generic form of the prescription drug Diflucan is often cheaper than OTC Monistat and works quicker and internally.

I learned all of this from my doctor after experiencing similar symptoms once and freaking out. However, I did some research to back myself up in case you need more proof and many of the sites I found listed ways to combat pH changes during your period leading to infection. This site is the most helpful I think in that it backs up what I said, lists ways to avoid BV, and isn't secretly trying to get you to invest in some certain brand of tampon: http://eon.businesswire.com/news/eon/20100217005268/en/Bacterial-Vaginosis/BV/infection

tl;dr-- pH changes during period often cause either BV or yeast infections and once you know what you have you can easily treat it.