If you have been having regular cycles prior to this, you could have conceived. The slight spotting you had could be the implantation
bleed. A home pregnancy
test can be properly read only 3-7 days after a missed period with a fresh early morning sample of urine. You may repeat the test after a couple of days or go for serum beta-hCG
measurement. This is confirmatory. Hope this information is useful. Take care.