Try not to let it derail you from your plan - that definitely won't help!
It can be hard not to let the scale affect your outlook, but if you are following the plan (getting in your GHGs, watching portion sizes, tracking, etc.) then focus on the positives; you are doing what you are supposed to and the scale will catch up. There are going to be bumps along the road and an isolated gain is not worth throwing in the towel over. One thing that helped me in the past is to look at my weight loss over the period of a month and look for patterns in my weight loss, rather than one individual week. I may have had a small loss one week, a gain the next, and a good loss another, and maybe another small loss, so I was still averaging a good loss for that period.
You might also want to look at your sodium intake. I have found that to be the culprit for me a lot of times - processed/prepackaged foods and restaurant foods are typically high in sodium.

Stay strong, you can do this!