Advice from runners needed please!

Hello fellow runners! Ive enjoyed outside running for quite a few years now, even if I dont run during winter from lets say november through march (I train on my own rower instead). I did continue to enjoy the great outdoors throughout the first semester. I shortened my runs from 8-9K down to 6-7K and slowed down my HR from 170-180 to 165-ish. However since I turned the 13 weeks mark, fatigue has taken over and I lack motivation, which has never really been an issue for me. My last run I stopped at 5K, HB around 160, and my pace went from about 5:30min/K to like 7min/K... Have anyone's performances drastically diminished like this? How did you cope with it? I mean, the less I exercice, the less good sleep I get, the more constipation problems I have, to more fat I feel... I feel the next 27 weeks are not gonna get any better. Any feedback is appreciated 😀