Hi Amit
The way to check the history of transaction used is ST03N/ Stad or one customize programme which need to maintain.
But there point which need to take into consideration is how your user mapping is there as is this one to one user or one to many user.
One to One user is that one user is in portal and same user should be there in GUI and one to many relationship is one user id in portal which is fetching all details from GUI means only this user id will be there in GUI as system or service id and managing all access in portal.
then you need to check all the details in portal UME as there is one activity report which will help you.
Thanks
Bhupinder Singh Arora