weight loss frustration

I'm hoping someone can help me out here. I'm 43 years old and had a
massive heart attack two years ago. After the heart attack, I began a
fitness program that eventually built up to about 5k of slow (7
mins/1k) jogging five times a week. I went from 185 pounds to about
165 pounds in just a few months and kept it up for a little more than
a year. Then I moved to a colder part of the country, found that I
couldn't stand jogging in the winter, and eventually gave it up. About
10 weeks ago, I joined a gym because my weight had once again shot up
to about 185 pounds. I've been doing 40 minutes of moderate aerobic
exercise five times a week with very light (10 lbs) weightlifting four
times a week. Although I've noticed an improvement in how I feel, I
haven't lost a single pound in the past 10 weeks. If anything, I'm
eating healthier than I used to, and I calculate my weekly caloric
burn at 2,500, or 10,000 calories a month, or roughly three pounds
every four weeks. I reckon I should have lost about eight pounds. What
gives? Have I gained that much muscle? Will I start seeing faster
weight loss soon?