Odd are you are pushing too hard from the start, so you run out of steam too fast. I speak from experience

I am not a strong rider; on flats I can do 'okay' but the minute I get to a hill I poop out. It seems that every source I've found agrees that they way to get stronger is to slow down....funny, huh? The point is that new riders (and I suspect people who used to ride a lot but have not in a decade) tend to try to go harder than they are able to do over a sustained period. They say the key to getting stronger is to do training rides where you stay in low gears, but keep a good fast cadence (aprox 90rpm). I just got a computer with a cadence counter in order to work on that.

I took a ride this AM who's goal was to work on hills, not to add miles or speed. I only did 9.5 miles. I only averaged 10.5mph, but I didn't have to walk any of the hills and by the end I was starting to figure out the whole 'keep the cadence up' thing.

So, maybe if you slow down, think about your cadencean d the beautiful spring days, rather than how far and fast you are going, you will have more fun and get better results.

Barbara