Infection causing fast heart rate and flare up

Hi everyone, I have recently been feeling really ill like I was taking a flu, and my doctor said i'd a sinus infection and gave me antibiotics. The antibiotics didn't work at all and I kept feeling worse, with joint and muscluar pain keeping me up at night etc so I went back to see the doctor who told me the infection has spread. All my glands are up im my neck, stomach and under my arms and I have a fast resting heart rate (I have NEVER had this before). He gave me another  antibiotic and I have to see him again on Friday to see if it is working. I am very concerned about the rapid heart rate- is this normal with an infection, and is it a serious problem? Also Is it likely the infection has caused the joints to become inflammed again? I currently take methotrexate, but due to the infection didn't take it last week and it looks like this week is a no go either. Im misrable at the moment- this flare up as you all know is horrible, however Its the infection that worries me incase it turns serious. Has anyone else had a fast heart rate due to infection and did this go away. Please help!