What Causes Rib Pain And Weakness In Leg After Taking Methotrexate?

I am on methotrexate 125mg by inject pen every week. I feel unusually tired and have pain in my rib area on my left side. Sometimes my legs feel very weak & I look very pale on a very rare occasion I think I look a bit yellow/waxy in colour. I have very hot sweats during the night and have to change my pajamas. 5 years ago I had septice which left me with rhumotoid arthritis. My dr did a thyroid test which was okay. Should I go back to my gp!