How much did you actually walk? Your weight loss number seems low.
You claim to have lost 18 pounds during the trip. There's about 3500 calories in a pound. That means you has a net loss of 18 * 3500 = 63k calories. 63000 / 148 days = 426 calories a day you need to burn to burn 18 pounds over 148 days.
A 180 pound person burns about 95 calories per hour of walking. You're a huskier dude, so I reckon you weighted even more than that. But let's just use that number (you'll see that it won't matter later). Walking 3100 miles over 148 days is 20 miles per day (I rounded down, it's closer to 21). Therefore, you burned 95 * 20 = 1900 calories a day walking.
Given your size and sex, a conservative estimate of your BMR would be about 2000. Therefore, your average total daily energy expenditure was 3900 calories.
Bring it all together: 3900 calories per day burned - 426 (you need a 426 calorie deficit per day) is 3474 calories.
3474 calories is quite a lot of calories to be eating every day on average. Now, keep in mind, I've been very conservative with my estimates. I suppose it's possible that you only lost 18 pounds, but you gotta admit it sounds fishy.