Oxyelite pro is mainly use to burn fat faster by increasing metabolism and so that it helps to reduce weight. However it is also having some side effects like muscle twitching, increased heart rate, constipation, decrease appetite, restlessness etc. Here you have complain you had increase heart rate. As well pain in back. It could be related to the consumption of oxyelite pro also. Oxyelite Pro is a vasoconstrictor, which shrinks the diameter of blood vessels and impedes blood flow. With an increased heart rate, vasoconstriction can increase blood pressure, which can increase one s risk for a heart attack or stroke. When used with exercise, this can be potentially dangerous. Hot Flashes: Some users of Oxyelite Pro have reported hot flashes. This is from the increase in thermogenic compounds which can increase the metabolism. The side effect of increased metabolism is sudden hot flashes. From all above data it looks like you had stomach pain due to constipation or hot flashes as well back pain could be due to muscle twitching and increased heart rate is already a side effect of oxyelite pro. Here I suggest to stop having it and follow a natural way of reducing weight like doing regular exercises as well maintaining healthy balance diet. This will be much better for your physical health too. In case after stopping this oxyelite pro still you have the same symptoms then I suggest to visit a doctor for detail examination of your heartand stomach health along with back issues. Take care.