There may be natural limits to any goal. The further away you are from the ideal, the goal, the faster you are at getting there, but as you get closer, your progress slows down. A very common mathematical phenomenon: The L-, or J-curve.

Specifically, switch up your routine. Find new muscles to exercise, like upper body. The more you exercise on the bike, the more efficient your legs get, and that means less energy burned, even though your legs, heart, breath are stronger and overall health better. Maybe 155 is fine for you…
References :

But also, if you lose a lot of weight, there is a bit of a weight plateu where you can do the exact same thing – or more! – and not lose any weight at all. This is because your body needs time to adjust to itself. Dropping 20 pounds just sent it all out of whack – in a good way! While you wait for it to settle down, just keep doing the same thing you’ve been doing to maintain your weight and keep losing after the plateu is behind you.
References :

Below is a link that explains what this is, much better than I ever could, and how to get over this ‘hump’ and begin losing weight again.

EDIT: Actually, scratch that, as the first page I listed was an advertisement for something. I have posted another one which explains it …

"If you’ve ever tried to lose fat for any sustained period of time – you may have hit a plateau. You have changed nothing, but suddenly the fat no longer disappears. The human body is incredibly adaptive, and will do its level best to maintain equilibrium (homeostasis).

The plateauing effect has to be the biggest motivation-killer there is. Unfortunately many popular diet books are strangely quiet on the issue — I guess the concept doesn’t sell well.

The best single word of advice is to make a change. DON’T MAKE THE MISTAKE OF DOING THE SAME THING over and over expecting a different result (Ben Franklin’s definition of insanity) …"
References :
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http://www.diet-blog.com/archives/2006/02/27/5_ways_to_break_a_weight_loss_plateau.php

but try to keep switching your foods dont eat the same amount of cal. each day cause then your metobalism ajusts to burn that much each day
References :

Cereal for breakfast

For Lunch, something filling like rice and beans or mashed potatoes

And for dinner, a healthy but decent meal like a plate of tomato slices etc.

Plus 2 hours of riding my exercise bike a day

So far I’ve lost 20 pounds in the past month while on this diet, I would lose about 5 pounds a week.

My overall goal is to reach 140 pounds but now that I’m at 155 pounds (I used to be 175), I can’t seem to lose anymore weight? I have the same routine, but all I’m able to do is maintain my weight? Should I do more exercise or lower my calories a bit?
TjB – I’m 15 years old and I’m 5 foot 10