Django SQLite application Error after some time sleep

I have a strange problem with Django. I have developed an application with Django, that is a database of papers. i used SQLite. the db has 8 field including title, authors and ... and has about 60000 records. Every thing is OK, but the problem is when i don't search in db through Django interface like a night, in the morning when i search something in db through Django, i get Error page is not working, while after some refreshing page and passing some mins it works greatly!!! i.e with every search results is shown quickly. Any idea.