Could this be overtraining?

First of all, thank you for reading this. I'm mildly worried about the possibilty that I've been experiencing the "symptoms" of overtraining fot quite a long time without acknowleding it. I'm working out consistently with Fitness Blender since March, roughly four to five times a week. As far as I recall, I've experienced muscle soreness only the very first weeks of regular physical activity, but then the soreness no longer came back. I always did feel fatigued after intense HIIT and very difficult exercises, of course, but not sore. Flash forward to these last few days: recently, I've completed my first FB program (taking it slow, because as I mentioned I only workout four to five times a week) and then I took a "forced" rest period in which I couldn't workout for days (roughly an entire week). Three days ago and again today, I chose to workout. I've started Sweat and...surprise! The soreness is back; in addition to this, I feel that I've "leaned out" when I stopped. I just don't get it. I didn't stop for such a long time that my body could have "forget" all that it learned, did I? The overtraining hypothesis seems strange as well, but I don't know what to think. I'd be happy to hear your opinions about this. Thank you again!