I bought a meyer Lemon tree about a week ago from a local flower shop. I live in New York City so I have no outdoor space but I put it next to a sunny window and have a grow light for when it needs more light. I noticed the past few days that there has been some sap on the tree. A branch seems to be oozing it.

Also I am not sure if near the bottom there is one large sucker.

The tree has fruit on it so I don't want to transplant it and I'm not sure if I should prune it or how.

I am attaching pictures of the sap and the possible sucker.

I appreciate all the help as a newbie :)