Stress, such as exam stress, can indeed have an impact on your menstrual cycle and potentially cause delays or irregularities. The symptoms you're experiencing, such as sore breasts and feeling emotional, are common premenstrual symptoms (PMS) that many people experience before their period.
The small amount of blood you noticed could be indicative of the start of your period, but it's difficult to say for certain. It's possible that your menstrual cycle is just delayed due to the stress you've been experiencing. However, if you're concerned about the irregularity of your cycle or if your period doesn't arrive within a reasonable timeframe, it's a good idea to consult a healthcare professional. They can evaluate your situation and provide appropriate guidance.
Additionally, keep in mind that there are other factors that can influence menstrual cycles, such as hormonal changes, changes in weight, certain medications, and underlying health conditions. It's always a good idea to discuss any concerns or irregularities with a healthcare professional who can provide personalized advice based on your specific situation.