Its actually 120 days not 90 days, check the back of the temp license. You should get it in lets say, about 2 months from the date of the skills test. If you dont, start chasing it from the third month.
You can also try
https://amsrvs.registry.faa.gov/airmeninquiry to see if it has been issued. A rule of thumb is to expect your license about a week from the date it was posted on the above site.
Another thing, the FAA have moved on from the paper license and you should get a plastic credit card looking license (It looks cool I must say).
Regards
DMan