Logically IF you haven't changed something, then something else has. Have you had dental work, amalgam fillings? something you dont necessarily associate with blood sugar that can effect it. Have you started supplements with starch fillers? etc. you get my drift, its detective work
Is your sleep quality good, you may have high cortisol levels. Dr Jason Fung said he isn't worried about blood glucose as such, its insulin levels that are important, especially if you are still insulin resistant. Check him out on youtube.
Or as others say, you may have inflammation/infection and your body defences are ramping up, along with the fuel to support it. Get some inflammatory marker test done by the Dr perhaps?
Good luck.