There could be a variety of reasons for this. Your mentor may be busy with other obligations, or they may have missed your email. It's also possible that they are still considering their response and want to provide a well-thought-out reply.
It's generally recommended to wait at least a week before following up. This gives your mentor enough time to respond without seeming pushy or impatient.
It's best to follow up with a polite reminder rather than simply resending the same email. Your mentor may have missed the first email, but resending without any context may come off as spammy.
If your mentor has provided you with other means of contact, such as a phone number or social media account, it may be acceptable to follow up through those channels after a reasonable amount of time has passed. However, always be respectful of your mentor's time and boundaries.
No, it's important to remember that your mentor is likely very busy and may receive a high volume of emails. It's possible that your email was overlooked or even accidentally deleted. Try not to take it personally and instead follow up politely.