Can I obtain a tourist visa in Thailand without leaving the country after my ED visa expires?

Suggest you ask an experienced Border run/Visa run service company in your area if they will take you ....either to do a BORDER BOUNCE or get a NEW Thai tourist visa. Here is a graphic FYI .

𝗜 𝘄𝗮𝘀 𝘄𝗼𝗻𝗱𝗲𝗿𝗶𝗻𝗴 𝗶𝗳 𝘁𝗵𝗲𝗿𝗲 𝗶𝘀 𝗮𝗻𝘆 𝘄𝗮𝘆 𝘁𝗼 𝗴𝗲𝘁 𝗮 𝘁𝗼𝘂𝗿𝗶𝘀𝘁 𝘃𝗶𝘀𝗮 𝘄𝗶𝘁𝗵𝗼𝘂𝘁 𝗵𝗮𝘃𝗶𝗻𝗴 𝘁𝗼 𝗹𝗲𝗮𝘃𝗲 𝘁𝗵𝗲 𝗰𝗼𝘂𝗻𝘁𝗿𝘆.

Alas there is not, there's no such thing as an in country tourist visa

So you have two choices, you're here on a 90 day ED visa based on interning which means you can't get that extended inside the country but can stay until the 90 day stamp you have runs out

Then you would either exit/re-enter thailand to get in on a 30 day visa exempt entry (free entry stamp) which you could extend one time in country for 1900baht

OR

You'd go to a thai consulate in a nearby country and get a single entry tourist visa which will stamp you in for 60 days when you return.

Those are your choices,