AdamDZ

Ludeart, I mean no offense but you may be simply out of shape. 3km isn't a lot so your best bet is to keep riding and getting stronger. As mentioned above: getting tired and sweating is normal. Some people sweat more, some sweat less. I can ride 20km without stopping but I'll sweat a lot. I always sweated a lot and I always will, that's normal.

Now, you may consider how that excessive sweating affects your ride and if there is a way to lower the sweating. Perhaps you sweat more than you should? If you're overdressed you will sweat too much, overheat and get fatigued. The idea is that you should dress in way that you feel a little cold when you start riding and you should warm up within 15 minutes or so. If you walk out with your bike and you feel nice and warm before even starting to ride that means you are overdressed. Overdressing leads to overheating and increased fatigue.

Next thing is comfort: you can be sweating and be comfortable. But if your sweating makes you uncomfortable that will lower your enjoyment and possibly lead to mentally induced fatigue. Rethink the way you dress. Invest in wicking base layer, avoid cotton, etc. Yes! Wool is the best for winter riding!

Does the sweating lead to physical discomfort, skin rash, etc? Again, that will cause fatigue.

Other things to consider: as others mentioned already, keep your tires pumped up hard and keep your bike in a good shape so it rolls easier, make sure you have proper riding position. Get rid of the dynamo and get battery powered lights.

Get regular, good sleep. Yeah, I know that's not always easy these days, but do your best.

Keep in mind that most people find it more difficult and harder to ride in very cold weather, that's also normal. Your body needs extra energy to keep warm, breathing cold air is hard and unpleasant too.

Pace yourself. Start slow and easy, let your body warm up, let your hart and breathing rate increase gradually and start pumping extra oxygen to your muscles. If you start pushing yourself too quickly you will "crash and burn" and won't be able to recover without extended rest period.

Don't eat right before riding. Give yourself at least 30 minutes after your meal before riding, the more the better. Your body uses extra energy and resources to digest your recent meal and is not ready for heavy physical activity.

Drink water regularly, not just before and during the ride but make it a point to drink water at least once an hour during the day, never let yourself be thirsty. If you're thirsty it's already too late: you're dehydrated. Thirst is a warning signal that your body needs something. Same with hunger: eat before you're really hungry and eat nutritious. You need to pee at least every two hours during your awake period. If it's less then you're not getting enough water. You may not feel any severe dehydration but it may be enough to make you weaker than you should be.

Make sure that biking isn't your only physical activity: do some walking, light running, stretching, weight lifting, maybe a hike or two a month, ride more, ride more, ride more.

Edit: About winter jackets. Ideally you'd get a jacket that is windproof on the front of the body and sleeves but provides some breathability through the sides, back and underarms. If your jacket is completely sealed off without ventilation you will overheat. Of course, the colder it gets the less ventilation you may need. But generally speaking typical winter jackets designed for walking don't work very well for serious cycling.

I hope this helps!

Adam