My girlfriend period is 1week late, never late, last p was 1/29 hasthryroid problem is obese. We had unprotected sex on2/10now late but tests negative?

Get checked. She should see her obgyn. If she truly had a period on 1/29 and is "never late" your unprotected sex may well have come at or around ovulation (egg release), thereby making pregnancy very possible. She should get a serum pregnancy test and a thyroid check. If she's pregnant, she wants to make sure her thyroid hormone levels are adequate to ensure the baby's healthy development.
Need Endo eval. Sounds that your girl friend needs to have an endocrine evaluation "hormonal workup". With pregnancy testing being negative, there could be other reasons for irregular menses (an occasional late period can be normal especially during stressful times) such as morbid obesity/insulin resistance and very low thyroid levels. Checking her thyroid level and serum beta HCG is needed.