You may have antibiotic-associated colitis. There's info out there on the web about it. Basically it's when the antibiotics kill off most of the bacteria in your guts and you either have problems because you lack the bacteria need to properly break down your food, or bad bacteria will take over all that empty space and cause you problems.
As far as I know, the only good treatment for a lack of bacteria in the guts is to take probiotics. That also works to help get rid of bad bacteria, although if you have a lot of them, you may need more antiobitcs to help get rid of them (doesn't sound like you're that bad off, though).
I have read that we normally get good bacteria from eating vegetables. I don't know, though, if they also carry bad bacteria and if washing vegetables or cooking them lessens the number of good bacteria we consume. You can always get more good bacteria from the pills than from veggies, although they're good for long-term maintanence and a lot of other things.
A lot of people who are lactose intolerant can eat yogurt because the bacteria in the yogurt consume most of the lactose before you ever eat it. I have heard, though, that the more expensive and organic brands have more bacteria than the cheap brands and therefore less lactose is present. However, if you have had a bad reaction to yogurt in the past, then by all means don't eat any; there are some people who are so sensitive they can't even handle a small amount of residual lactose that's in the yogurt.
From what I have read on the internet, some doctors prescribe not only probiotics while on antibiotics, but say you should keep them up for a week or two after you get off the antibiotics to give your guts a chance to repopulate the bacteria. One doctor I read said also that he put his patients on three-four times the normal dosage of probiotics while they were on antibiotics and like twice the dosage for the week or two afterwards. Since the antibiotics kill off everything--including the probiotics you're taking--it makes sense to really up the levels you take in order to get the odds in your favor that some will survive. As far as I am aware, you cannot overdose on probiotics, so it really doesn't matter how many you take, with the exception that taking too many can cause excess gas and cramping until you adjust.
You can also try taking Caltrate 600 w/Vitamin D for the diarrhea. It absorbs excess water in the colon--keeping you from getting runny--and there is some evidence that calcium can help soothe and heal the intestinal lining when it gets inflamed or irritated from things like bad bacteria. I think you can safely take up to three pills a day (the normal doseage is 2) in order to get your diarrhea to stop. The calcium may also help with your heartburn, but you may need to take something specifically for it until you get your lower guts straightened out.