A colon cleanse is not a good course of action, because it doesn't get rid of your bacteria; it's nothing but a laxative. You might flush some bacteria out, but because bad bacteria is notoriously hard to get rid of, you're more likely to flush out what good you have in there, I think, than to flush out bad.
Has a doctor told you that you have abnormal amounts of bad bacteria? We all have some, but it's only a problem if we have too much. The probiotics will help, but the general course of action if you have a bad bacteria overgrowth problem is to take specific antibiotics (not just any antibiotic will do) and to also take large doses of probiotics. The bad bacteria can be hard to dislodge and most people would rather do a course of antibiotics and be hopefully be done with it; taking nothing but probitoics may require many months to overcome the bad bacteria, if it can even do it alone.
Yes, antibiotics kill off good and bad bacteria in your guts, and yes, your old regimen of antibiotics may have caused the problems you have now. There's actually something known as antibiotic-associated diarrhea and antibiotic-associated colitis, and both are caused by the antibiotics causing an imbalance in your intestinal bacteria. However, even though antibiotics may have caused the problem, it is usually to them that you have to look to also fix the problem. Only this time, take lots of probiotics so you can get yourself back in balance. Now that I've learned how antibioitcs and probiotics work, I never take an antibiotic for anything unless I am also on a probitotic pill at the same time, and then I take at least one Activia yogurt a day for about three weeks after I stop the antibiotics to get things straightened out in there.