Overheating almost everyday

Hi everyone! My marathon training starts in May, but I've been trying to maintain a weekly mileage of 33-40 km (over three runs) before officially starting. However, these days, my body feels hot most of the day. I also swim, play basketball, and do strength training on the side, and I commute to university on foot ( just 1.5 km). I have one rest day per week.

My watch shows that I’ve averaged 15 km per day over the last two months. I’ve also noticed that my resting heart rate has increased from the lower 50s to 65. Do you think my body isn't strong enough, or will it improve as I continue training? Looking for advice!