What Causes Delay In Periods,nausea And Lower Abdomen Pain?

hi, i was 10 days late thinking that I had missed my period over this time i am feeling over happy, have sensitve breast especially when i shower sore lower back i felt nauseas and still do im always urinating constantly light cramping in lower abdomen , sometimes feel dizzy during most days and im always hungry. but then I started what I thought was my period but it only lasted three days and was very light not enough to use a tampon but enough for a liner on then it just stopped 1 days later i got it a gain but this time it was for 2 days but it started of browny looking and finished a light pink colour , I have always been on time no later or early I am 29 yrs old my normal cycle is 30 days 21st of every month with out a miss except for this month, i took a hpt of later or missed period but it was a neg im so confused as to whats going on can you please help me understand.