Could a friend of mine be pregnant if her cycle came the 5th, ended the 6th, came back the 7th, went off the same night? Her cycle normally last 7 days. She have nausea, frequent headaches, tender breast, weight gain and sleep a lot.

It's possible... some women will have some spotting or bleeding in pregnancy, especially early on, thinking it is an irregular period. Of course, it could actually be just an irregular period. If she's been having nausea, headaches, increased tiredness, etc, she should either try a home pregnancy test or see her doctor for a test in office.

If she is having sexual intercourse then pregnancy is always a possibility. It is hard to tell whether what she experienced was her regular period or just spotting. Its time to take a HPT.