My girlfriend hasnt had her period in over a month but weve taken to pregnancy tests and they both said not pregnant, is she pregnant, what do we do?

Missed menses. Skipping a period does not always mean you are pregnant but you should seek further medical advice if you are getting a negative test. Sometimes bloodwork can be done to check. Stress, increased exercise or increase/decreased weight, are other reasons to miss a period but there could also be underlying medical conditions too that should be further evaluated.
Skipping period ok. If pregnancy test is negative she isn't likely pregnant. Usually we start looking into the cause of not having a period after 3 missed periods. Otherwise it is likely to be hormonal. If she is on birth control pills are hormonal birth control is is totally normal to skip a period while taking these. Some people when they know it is normal prefer it, but if not the pill can be changed.