Implantation or gas?

I've heard that implantation can feel like a cross between menstrual cramps and gas (is that true?). How long does that last? I'm 8dpo and I've been feeling bloated and an ache (either gas pain or dull cramping) for the last 2 nights and felt nauseated at night. The nauseous feeling started being a nightly thing about 2 nights ago. I occasionally feel a flutter in my abdomen, but that could be chalked up to gas as well. I have been very tired lately, so much to where I wake up confused as to which day it is. Even coffee won't wake me up fully. I feel winded and light headed more after walking up the stairs... This is my second month TTC for baby number 1. My main question is.. For those of you who are pregnant, is this feeling in line with implantation or does it sound like a typical stomach bug? I'm not sure what implantation is supposed to feel like and when symptoms typically start.