What Causes Delay In Periods,cramps,enlargement Of Breasts And Soreness?

Hi, i have been on the implant since early Nov 10. As well as the the usual side effects ive experienced over the past months, it finally started to get better. I have always had regular periods and even with the implant in i have never missed a month. Currently, as far as i remeber my last period was the week of the 10th May. It still has not come. I have all the symptoms, like bigger breasts and soreness, period like pains, i have been very moody and emotional, this has been going on for the past week maybe a bit more. My last recorded period was the 19th March, then it came early in May but now nothing. I have taken a pregnancy test and it has come back negative. I know how my body works and apart from the above symptoms, i dont think my period is coming any time soon. Is it possible that i could be pregnant but not show on the test? i have read blogs and have seen that 1 lady had the same as i did and she ended up being pregnant even though the tests she took all came back negative. I am stressing over this as i know this is irregular for my body but am getting no answers from the home test. Any advice would be greatful!