Feeling awful!

Could I feel any worse? ? I came off the pill in May, normal periods before and after! I had sex on the 19th august and my period on the 25th August (only last a couple of days tho but was normal colour) had sex again on Sunday 11th September,  been feeling rubbish since the Monday!  Today is worse, absolutely shattered,  back ache, stomach cramps are unbeatable,  feeling sick but also wanting to eat all the time,  peeing all the time but very constipated!  Can anyone help, could this just be waiting on my period which Is due a week on Thursday!