Quick answer: pregnancy can cause tiredness and cramping, but so can many other things. Detailed answer: In my experience, I would consider pregnancy as a strong possibility if you have had sexual intercourse without using effective birth control, particularly if your period is late or you have missed a few periods. If your periods are regular but heavy, you might be anemic (low iron). Tiredness and falling asleep and cramping can also be caused by underactive thyroid gland (hypothyroidism). You can do a pregnancy test yourself, or a primary care physician can do some tests including pregnancy test, and blood tests for anemia and thyroid. A primary care physician can also speak with you about safe and effective birth control. I hope this is helpful for you.