I'm a 17 year old girl. I started riding in November, and I don't know how to keep improving—I'm a bit lost. So I will describe my journey up until now and maybe you can help me.
One day my friend invited me to ride to a park. It was 10km, and it was awful. After not even 3km, I wanted to throw away the bike and grab an Uber. When I got home, my dad explained me that I had flat tires, so I guess it was a combination of being extremely unfit and that my bike was not in proper condition.
After that, I kept doing 4km (at about 17 km per hour) 5 times a week. Those rides were tiring but not impossible. Eventually they crept up to 8km (by accident: I would ride while shopping). Then I got interested in trying that 10km to the park again. I did it with my dad, and it was surprisingly easy. (We were going about 15km per hour.)
So I started doing 10km, but on a route without cars, so I could see how fast I could go and if I could maintain the speed. I did that during all December (at about 18 km per hour). It felt great. Sometimes I ran out of breath, but I could maintain it. (I also have chronic sinusitis, so I figured that is mainly the problem.) On December 31, I decided to do 20km. I did them in a bit less than an hour. I was tired after, but I did not struggle that much. I was extremely happy after.
Yesterday on January 7th (a week later) my boyfriend asked me to do 30km with him. I agreed because if I could do the 20km going "fast," then I could do more if I kept my energy and went "slow."
Here's the problem: he and his friends are VERY fit. I could keep up for the first maybe 14km, but after a 30 meter hill I was kind of exhausted. Then we slowed down and I completed the trip but very slow. The last 16km took us 1 hour (when I had done 20km in less than an hour before). I'm proud that I could do it, but now I'm a bit sore, and won't recover or be able to ride again for about a week at least. So I think that maybe I wasn't ready to ride that much.
What do you think? What should I do now? I don't know how much and how often I should ride between 10km and 30km to reach my goal: riding the 30km faster on a stable speed.
Also, here's a picture of my bike. It's a Halley classic 4x4 and has 18 speeds. It's very cheap, and comparing it to my friend's (that are much more professional mountain bikes) it feels like crap. But I wanted to be more fit before buying one.