Don’t know for sure

It’s been about three weeks since my last period and I’ve been watching videos and reading articles I have the majority of early stages of pregnancy but none of the test came back positive and I really don’t know what to do we want to have a baby and we have tried my belly is tight and I do feel tired and nauseous after I eat or drink anything I need some advice on this I’m hearing that I might need to try one of the more expensive tests I’m so confused.