6 days late but bfn?

Georgia • 20 years old, married military wife 🇬🇧🇬🇧
So I'm 6 days late for my period. I tested at 2 days late and then 4 days late and got a bfn. I'm having weird symptoms like back ache, feeling sick, nausea, constipation and very gassy. I know those symptoms are also linked with pms but I don't feel like I'm going to come on my period. Usually I have really bad cramps for a week before my period, I've just been having the odd cramp here and there and that started about 5dpo. I'm just wondering if I should test again? Have any of you been pregnant and got negative tests? X