I can barely wear a bra! Is it too early for symptoms?

My husband and I have been trying to conceive for a few months now and I'm 5-7 days past ovulation, (I ovulate a little early and have short bleeding phases, this month I only bled for three days) and my uterus (around that area) feels heavy and crampy, like when I'm on my period but I'm not on my period. My breasts are tender and feel heavy and my nipples are extremely sore. I can barely wear a bra! My period isn't due for another 12 days. I only work for 5 hours a day (I'm never on my feet at work) but I've been feeling so exhausted when I get home and during my work shift, and sometimes slightly lightheaded. Is it too early to have these symptoms? I have 10 miu/ml hCG tests, how soon can I take one? I feel really confident that I'm pregnant and I can hardly wait to test!