Ladies I need HELP

Jazmin

My new born got her 2 months shots today and I think she has a fever... I don't have Vaseline to check her thru her butt... I've totally 4got all this baby stuff lol 1st born is 7 so that 7 years ago I've been thru baby stuff lol I'm starting all over again and I checked her arm out but she cries and moves a lot... what s a best way to check her temp?