I accidentally drank 100mg of Clomid (clomiphene) on day 5, can I start back on my 50mg tomorrow? Or just continue 100mg?

Call your doctor. If 50 mg daily was prescribed, and if you are really unable to get in touch with your doctor, go back to 50 mg tomorrow and stay on it. Do contact your prescribing doctor if possible, he/she may prefer you to do something different. You aren't going to cause yourself any harm either way.