Maybe the two of are putting too much effort in and you're simply nervous. Take it slower and go at a pace that makes you feel comfy. Good luck
you could just be nervous and need more time,,, before penatration try other things like cuddling, touching, massaging, try oral sex before to get in the mood and slowly build it up, Its one of those things , if you've never came before with a guy you dont know what to expect and your body is holding you back like nausea.. it will happen patience is the key but like I say, oral sex is a good start on each other and patience. It will come around,,