Dear Karen,
From your post you sound like a very active person. Now you know it is not uncommon for female athletes to loose their period because they are so physically fit. You said you get cramps when you walk alot, when mostly anyone would get cramps if they walked alot. You also said you where going to that bathroom more often which is also normal for one who does alot of physical activies. When you are active you take in more fluids and your metabolism speeds up, in resulting of having to pee alot. With the nausea it’s the same thing, to much of a work out ( i.e running) will make you sick to your stomac and or vomit. Also because your period was a week late when you took the home pregnancy test and it was negative leads me to believe that you are not pregnant. Home pregnancy test are very sensitive, only needing 40 ml of hCG to detect pregnancy which occurs on the first day of your missed period, if you were pregnant you would be 5 weeks along which is very detectable by a home pregnancy test. I do still recommend seeing a doctor if your period doesn’t return soon just to make sure that nothing is wrong.
Best of Luck
Love, Falon