According to Timatic, you will not need a visa for Mexico, since you already have a valid US visa.
Visa required, except for Passengers with a valid visa issued by
Canada, Japan, USA, United Kingdom or a Schengen Member.
Will there be any problem while re-entry to US?
This shouldn't be a problem either. That's what "multiple entry" means. Of course, as a foreign national you may always be subject to some scrutiny at the US border, and you're never guaranteed to be allowed entry. However, in this case it will be your second entry on the visa, and you should not be worried. As long as you follow all rules and don't do anything to attract negative attention, there shouldn't be a problem.