First and most important: Congrats on keeping riding your bike and quitting smoking!!! These two improvements are going to pay you back for the rest of your life no matter what else.
A resting heartrate of 100 is surprisingly high, especially for someone who is a regular exerciser. I'd look into that.
I'm also surprised by your dietician's recommendation of 1550 kcal/day for weight loss. At 230# that is almost certainly below your basal metabolic rate (guesstimate 1750 kcal/day, a little more or less depending on your height and age). Even if you have a totally sedentary job, you should be using 2200 or more kcal/day without any exercise, and a slightly higher intake (say, 1800) SHOULD still allow for slow, steady weight loss for you.
There are a variety of metabolic syndromes that could be at play here. Polycystic ovaries is one that springs to mind right away.
Suggestion: dedicate yourself to making a totally accurate food log for a week. Don't lift the fork until you've lifted the pen to write it down. Measure quantities - so that you are sure of what you're getting. Then calculate out your calories.
Don't look at this as a suggestion that you're overeating - it's not. You just need accurate data so that you know (a) how many calories you're really eating, and (b) whether that translates to weight loss.
Now that you've got a good figure for calorie intake, see if it's a reasonable proposition to dedicate the time and energy to burn off 25% of the calories you're eating through exercise. Example: if you're eating 2000 kcal/day, make sure you burn 500 kcal/day through exercise. This could be something like 15 miles of biking, or 4 miles of walking/jogging.
If you're eating normally (consistently less than 2500 kcal/day) and burning off 25% of it through exercise, and you're not losing weight, suspect a medical reason why you're having trouble losing weight.
If you can't imagine burning 25% of the calories you eat through exercise then you may be eating too many calories to sustain weight loss.
Good luck and stay connected!