Run this to see what's been using Tempdb and how much space is allocated to that session

-- how much was allocated and by what user

SELECT

sys.dm_exec_sessions.session_id as [Session ID],

DB_NAME(database_id) as [Database Name],

host_name as [System Name],

program_name as [Program Name],

login_name as [User Name],

status,

cpu_time as [CPU Time (in milisec)],

total_scheduled_time as [Total Scheduled Time (in milisec)],

total_elapsed_time as [Elapsed Time (in milisec)],

(memory_usage * 8) as [Memory Usage (in KB)],

(user_objects_alloc_page_count * 8) as [Space Allocated for User Objects (in KB)],

(user_objects_dealloc_page_count * 8) as [Space Deallocated for User Objects (in KB)],

(internal_objects_alloc_page_count * 8) as [Space Allocated for Internal Objects (in KB)],

(internal_objects_dealloc_page_count * 8) as [Space Deallocated for Internal Objects (in KB)],

case is_user_process

when 1 then 'user session'

when 0 then 'system session'

end as [Session Type], row_count as [Row Count]

from sys.dm_db_session_space_usage

inner join

sys.dm_exec_sessions

on sys.dm_db_session_space_usage.session_id = sys.dm_exec_sessions.session_id

Then match the spid to this query, check the query_text and query_plan, you'll find out what's eating all your space

select top 10

t1.session_id,

t1.request_id,

t1.task_alloc,

t1.task_dealloc,

(SELECT SUBSTRING(text, t2.statement_start_offset/2 + 1,

(CASE WHEN statement_end_offset = -1

THEN LEN(CONVERT(nvarchar(max),text)) * 2

ELSE statement_end_offset

END - t2.statement_start_offset)/2)

FROM sys.dm_exec_sql_text(sql_handle)) AS query_text,

(SELECT query_plan from sys.dm_exec_query_plan(t2.plan_handle)) as query_plan

from (Select session_id, request_id,

sum(internal_objects_alloc_page_count + user_objects_alloc_page_count) as task_alloc,

sum (internal_objects_dealloc_page_count + user_objects_dealloc_page_count) as task_dealloc

from sys.dm_db_task_space_usage

group by session_id, request_id) as t1,

sys.dm_exec_requests as t2

where t1.session_id = t2.session_id and

(t1.request_id = t2.request_id) and

t1.session_id > 50

order by t1.task_alloc DESC