Sammi,
From a former physical trainer, let me say that the biggest thing I hear in your posts is your self doubt that what you are doing isn't as good as what others may be doing. That line of thinking can hurt you a lot. What I see from your post is that you quit smoking, are getting in shape, are riding your bike 4 miles up and down hills, are eating right and it definitely sounds like you are on the right track to a new, healthier you! HOW AWESOME IS THAT?!?! Please, don't worry about how fast you're going or that you can only go 4 miles... 4 miles is AMAZING!!! Personally, I'd rather SWIM 4 miles than bike it (I don't do well on 2 wheels... I barely function on 4 - i.e. my car! LOL!) So even to me, 4 miles is great! And everybody has to start somewhere, and what's important is that you ARE starting!
Just remember that each time you ride your bike, it should take at least 20 minutes... 30 is better. I used to teach water aerobics and some ladies in my class couldn't exercise for even 15 minutes without feeling out of breath and miserable. So, I started them off at 10 minutes and worked up from there. So, if you're still at a point where you are having a hard time with a whole 30 minutes, that's OK... but it's important to work up to that point soon.
Also, when you exercise, you want to stay within your target heart rate range. I don't know if you know these things already... if you do, then great! If not, here's some help. Take 180 minus your age. Then multiply that by .8 That's the top of your range. You don't want your heart rate to go above that. Then, multiply that same number (180 minus your age) by .6 That's the bottom of your range. You don't want your heart rate to go below that number when exercising (except in the beginning, you might not be able to get there right away, and if that's the case, that's OK... but work up to getting your heart rate to that number as soon as you can). When you take your heartbeat, clock it for 6 seconds and multiply by 10.
If you went back several months and read various posts, just out of curiosity, did you read the "ME" tabalism post? I'll bump it for you. It talks about how to eat for your metabolism... oftentimes, just cutting caloric intake isn't enough. You have to cut the RI