Is it possible for only several weeks of consistent training to start causing overtraining syndrome?
Yes, because…
I’ve been training consistently for really my first time ever. Before this, I was not sedentary but I was extremely inconsistent.
Your body is trying to figure out what’s going on… It sounds like it needs a rest. The good news is, if you are showing signs of overtraining, you’ve identified it right away. After a super easy week, you should be fine.
Cut your volume in half for the recovery week and see how you feel. If you’re still not right, take another week.
Also… 36′ of intensity on only a handful of weeks of training is way too much. In general, you want to limit your training above aerobic threshold (that’s aerobic, not anaerobic) to 5% or less. So on a sustained volume of 10 hours per week, 30′ might be appropriate. For half that, half that.
But because you’re new to training, you can safely avoid it altogether. You’ll make plenty of gains just by being active on a regular basis in a structured way.