7 days periods are fairly long periods. 3-4 days are a more "common" duration for periods. However, the fact that it starts and stops is more unusual.
You should contact your doctor to check your uterus lining and cervix. If everything is in order, it can be simply caused by fluctuations in your hormonal levels.
Stress, big changes in the diet, some supplements or medications can provoke such fluctuations. If it is the case, you can wait a few months and see if everything returns to normal.
If it does not calm down, taking Vitex from Vogel can help regulate hormonal levels.