Cramps are not considered a hargashah. Hargashah is not well defined in written halachic sources. A number of possibilities are described:

she feels her uterus open

she feels her whole body shake

she feels an internal flow.

Menstrual cramps do not fall into these categories.

If your cramps come regularly, and you always see blood at at the same interval following the cramps, you may have a veset haguf. We suggest you read about these two concepts on our website, where they are discussed at length, and get back to us if you have a more specific question.