First point, if you only train till you're tired you won't get better. It's doing that next set when you feel like shit that's going to make you better. Push another one out each time till you get used to it, then add another, and another, etc.

Second point, do planks for your abs and obliques. Much better than crunches.

edit: forgot to mention, it's ok if you vomit, intact it's preferred. It's how you know you've pushed yourself, lol.

Well I'm currently working out 6 days a week now, only resting on Sunday. I do 80 burpees on Monday, and then 100 pushups on Tuesday, and then the cycle repeats over and over until the rest day.

I plan on raising the number of burpees to 90 on the first of April, and raise the pushup count to 120 as well.

Had a chance to go back and reread your original post, so I can answer better. To be more detailed, how old are you, are you more genetically predisposed to have a gut, or abs. What's your body fat at right now? Depending on how close you are now, 2 months may or may not be possible.

HIIT is better for developing increased cardio capacity, and not necessarily better for fat burning because of the tempo and duration. Good old fashioned long distance running at the right pace can be better. So perhaps mixing those two together, will help hasten your approach.

Burpees I've discovered are good for one thing, losing your lunch, lol. They are great for mixing into yor cardio routine, but as far as developing strength and muscle, I've not had good results. You also mentioned an issue with your back, is it just from doing crunches, or does it bother you at other times?

I'm not much for calorie counting, as when I cut, I eat clean, and eat till I'm satisfied. When I bulk, I eat till I'm stuffed. And I always eat at least 5 meals a day. So I can't really help there. I can generally guess my body fat by looking in the mirror. Around 14% top abs start to show, below 12, they are all poking through, 10, get the camera out. Of course that's a generalization, because a friend of mine was at 14% i think, and had a nice b cup.

With the dumbbells, try to incorporate multiple movements into each rep, especially if they are too light. Otherwise look into getting a barbells and some plates. Craigslist is your friend. Hitting the legs won't really help with the endurance, just the power and speed, but certain lifts will impact your entire body. All to often many men neglect their legs and look weird. Who cares if you have 18" arms, and 16" legs? Some of the most physically appealing men have well proportioned bodies, but that is a whole other topic.

I've seem to rambled on, I can talk about fitness forever...