Is there a chance I could be pregnant?

My husband had a reverse vasectomy just over a year ago. The doctor said everything went well and he still had viable sperm, but we didn't bother following up afterwards because we figured we'll either get pregnant or we won't, nothing can be done either way.

I've been off the pill for two months and my cycle is all over the place. When I first went off the pill, I didn't get a period for almost 6 weeks. It's now been a month and I feel like my period is coming, because I have cramping and a very sore lower back.

However I also had a bout of getting sick about a week ago, have had this weird taste in my mouth (not metallic like I did when I was pg with my first, just...bad!), and I feel like crying ALL THE TIME. Over everything. I have felt emotional from time to time when pmsing, but rarely.

If I had a regular 28 day cycle, my period would be due today. I took a first response early result test yesterday and it was negative. Now I'm feeling discouraged thinking my period is definitely coming and I'm imagining all these symptoms, because the cramps definitely feel like they do when it's about that time. Except they've been more focused on my left side (my back ache is more on the left side too).

I guess I'm wondering if there is any chance I could be pg given it feels like pms and I got a negative test?? I'm going crazy here. Thanks!