Could this be implantation spotting?

Hey ladies. I'm 6 days late about 17-18 DPO I think. I just got back from a major road trip and read that traveling can screw up timing of ovulation so I could be wrong on my timeframe for DPO. I've been feeling sore boobs, sore back, a little irritable. And slightly nauseous the past two days. I've been spotting like this for about 3 days off and on and not enough to hit a pad. I took a test today and it was negative. I'm not stressed about it. Just a little confused on what the deal is. What do you guys think?