I know a lot of you will say go to your doctor and not buy online etc but I have had acne for over 20 years and things are finally getter better due to taking a small dose of amoxycillin twice a day. This is the only thing that has worked for me and I've been near enough clear for nearky a month. Doctors won't prescribe these as they're not supposed to be used longterm but those that are in my opinion are rubbish. I order my amoxycillin online and the strength is 250 . With all the side effects from accutane I don't think these are that bad apart from probably making you ammune to them. As I said ive been clear a month so don't know if it will last but I've had a very happy month 
It's not so simple as "it works so what's the harm." I guess that you understand and except the risk of buying drugs online. I should warn you that expired antibiotics are more dangerous than other expired drugs and there's no guarantee that you're getting what you want. The biggest problem that I could see is that your taking a low dose of antibiotics could mean that you could get an infection that's susceptible to amoxicillin and a sub therapeutic dose could let it go undetected until it becomes dangerous. You could get a uti that moves to your bladder and eventually your kidneys and then you'd be in big trouble. It not likely but bad things could come from this.
I understand your frustration with failed or unsatisfactory treatments. I took antibiotics on and off for 16 years and still ended up taking accutane. If long term antibiotics are are necessary then get it from a doctor, sulfamethoxazole/ trimethoprim (Bactrim) is an excellent drug. Btw, don't rule out accutane because of alleged side effects. Some are real and most of the others are complete bullshit.
I hate to preach because I've had the same impulse to side step the dermatologist and all the cost and hassle that comes with it. I just hate to see anyone make a bad decision even if it's for the right reasons.
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Thankyou for your feedback , it is much appreciated. I plan to come off these soon and go back on my other antibiotics prescribed by my doctor but I know I'll be back to square one. My acne is only mild to moderate so accutane wouldn't be an option for me but it's enough to ruin my day to day life 