I'm CONSTANTLY sick & antibiotics NEVER seem to help. What's wrong with me?

I am ALWAYS sick. I would say a good 20 (if not more) of 30 days of each month consist of me being sick. Sometimes, its a headache. Sometimes, its a sore throat. Sometimes, with stomach pain. Sometimes, its a mix. I'm ALWAYS going to the Dr to get antibiotics. I will usually feel better for a day or so, then feel worse again. Most of the time, the Dr. doesn't know what's wrong and he basically just UMES its what I suggest. Strep throat, sinus infection, etc. A couple years ago, I had 5 sinus infections in 6 months. Not fun. I also don't poop regularly. For me, its normal it poop about once every 5-6 days. That is normal. Has been for as long as I can remember. I am 21 right now. My mom said she use to make me eat about 40 prunes a day when I was young just so I could poop about once a day. Now, I have to eat like almost a whole box of Raisin Bran and that Activia Yougurt to even get close to going that much. It's not that I can't go, I just don't have to. I am also like always tired and out of energy. I came across something called "candida albicans" today and it got me thinking. Maybe I have a yeast of some sort growing in my body that is making me ill ALL THE TIME and maybe when I take the antibiotics, it makes it worse. Has anyone heard of this or does anyone have similar symptoms and could give me some advice on how to make me better? Thanks.