I cannot login with my user information

I keep trying to login using my username and password, but it keeps saying that I am not using a valid username. I have checked closely over a dozen times to make sure I had everything right, and of course I did. So, I logged in using another employee’s user info and changed my password, and even then I wasn’t able to login using the new password. I finally deleted myself as a user after logging in with my co-worker’s user info. From there, I deleted myself as a user and created a new user for myself. Then, everything worked fine for a couple of days, but now I am having the same thing happen again. I cannot log in to save my life. I tried the “lost password” option, but when I put my username or email in, it still says invalid username or email. I am so mad at this….Please help!