Ahh, I remember the days when I thought 3000 caps made me rich.
Oddly enough, I had the same issues as you when I played Fallout3, Aadrian1234, I was broke as [censored] all the time and allways desperately low on ammo, wasnt fun at all. The joys of this game is that there's so much stuff you can simply grab and sell, and people are so eager for it!
Fighting random raiders is a good way to make money, because armour, early on, sells for a fair amount in goodsprings.
Might be an idea to increase your barter skills if you have money flow issues. Also later on there's a perk you can take which increases your chances of finding ammo, it's actually pretty good! I havent had to buy much in the way of normal ammo for some time.