How long should implantation pains go on for?

i think i have been getting implantation pains but they are on and off (once a week or once every 2 weeks) for the past 3 or 4 weeks, my have got a little bigger and my belly seems to stick out a little more, i have been having more ween 2 (burping and farting oh and some hick-uping) and i have also been feeling a little sick at times (no vomoting just feeling and tasting it) and having a funny taste in my mouth, i am 2 and a half weeks late (no period), took a test a week and a half ago but negative although they said it i may be very early on (this was before i starting feeling all this), please can i have some of you advice?