Hi,
First of all i wouldn't worry about it. I have a few questions though before i can help you. How long have you been having periods? how long do they usually last? have you ever missed more than 2 periods in a row?
The pain on your left hand side may be your ovary. When we ovulate it is usually alternate ovaries each month, so if it was your left last month it may be your right next month etc.
i hope this helps
Ok thank you :) do you know how much pregnancy tests are roughly?
Have you take a home pregnancy test? Any time you are sexually active and have an off period that is different than normal, you should always test just to make sure you are not pregnant. It could just be a side effect of the pill or might be ovarian cysts, but you want to make sure you are not pregnant first. If the cramps are very painful, make a doctor's appointment to find out what is going on. Take care.