How challenges winning XP is calculated?

You have so big experience in weapon that usually 6px is most what you can get.

You can learn another language and do challenges there; because you haven't got a lot of weapon xp there yet, cash will flow more freely again - for a while. When all the weapons have dried up, there's only one way: Challenge a million times for only 5 points as quite a lot of sololearners seem to do. It actually sums up remarkably. Maybe you want to take a look at this: https://code.sololearn.com/WouWz5g1A4ed/?ref=app

What can I do now

You will win more xp's only when you will beat your equivalent oponents.

The winner gets certain amount of xp which is specified when you accept a challenge.....you will be rewarded one xp for each correct question and if you win you get additional xp mentioned at the beginning...

There's Elo system. If you win too much, you will only get good exp from people who also win too much.

I'm a bit rusty in Python and now when I lose challenges, I lose like 30xp. And when I win, I maybe get 5. What is that all about?

Yes, but I seem to l lose a lot even when challenged by higher level opponents. For example, I lost 3:4 to a level 10 and lost 16xp. I'm level 6... what do you mean by Python xp? like how many challenges the person completed? or how far they got in to the sololearn class?

If you look up the skills section in your profile, you'll find separate xp for separate languages, aka 'weapons'. That's what decides the points you win or lose in a challenge, not your overall level.

Sololearn doesn't understand you're rusty. It just compares your Python xp to your opponent's Python xp and determines the favourite - you.