It's pretty typical for kids to cry for 10 or 15 min fairly often at drop off time in the morning - sometimes into the 2nd grade.
It's just what they need to do in order to deal with the transition from home to school.
At the pre-k school my son went to, they had a window where parents could peek into the room while their kid had no idea parents were watching.
Usually 15 min of crying ends and they go on to have a great day (and then when it's time to go home Mom comes to get them and they want to stay longer and play - so we get this both coming and going).
It's a great relief to know that the show for the purpose of showing loyalty to mom is usually very short.
It can take several months for kids to get into a good routine.
Potty accidents are also common into 1st grade - so I wouldn't worry too much about it.
Most day care/schools want a change of clothes kept at school so they have clean things to wear.
When he's calm, ask him who his best friend at school is and every day ask him what was the best thing that happened at school.
Tell him he's so lucky he gets to play at school and learn new games with his friends,
it's so boring at home and he's not missing anything.
Tell him you want the mornings to have less fussing so everyone has a great start to the day.
Get as much ready for the next day the night before (lunch/snacks, change of clothes, etc).
If he ever has to stay home sick - make sure it IS boring - he stays in bed and sleeps and the tv doesn't get turned on until the usual time in the evening like every other day.
In the morning, try to give your hug goodbye at home before leaving for school.
Once at school it's all business - make drop off as short and sweet as possible.
A quick "Ok! I love you! Bye bye!" and leave.
He'll make his transition quicker that way.
It's a tough stage but he will out grow it eventually.