Hi Aneesh,
please also check the document flow of your invoice. There you see as well, when your document is not posted. YOu can navigate from there to the Unposted source document.
Just to add to Lokesh's reply - it is a good advice to check the "work" lists regularly to ensure, that no relevant documents are waiting for your reaction (e.g. in Supplier Invoicing you see the not released invoices there, in paybles you see the payment proposals and clearing tasks, in G/L unposted source documents, etc.)
Best regards
Marlene