SQLite PRIMARY key AutoIncrement doesn't work

I'm trying to a have a table with an auto incremented primary key. The SQL query for table creation is included.
Problem is the auto-increment does not work. Meaning when I insert a row with NULL as the value of conversation_id it just inserts null. I have this problem on multiple tables.

-- Table: conversations
CREATE TABLE conversations (
    conversation_id INTEGER (64) PRIMARY KEY
                                 UNIQUE,
    target_id       BIGINT (64),
    sender_id       BIGINT (64),
    status          STRING (16)  NOT NULL
                                 DEFAULT unseen,
    is_group        INTEGER (1)  NOT NULL
                                 DEFAULT (0),
    last_update     INTEGER (32) DEFAULT (0),
    target_name     STRING (64),
    target_photo    STRING (256),
    unread_count    INTEGER (10) DEFAULT (0),
    last_message    STRING (256) 
);

The following is the method I use to insert into table:

public Conversation addConversation(Conversation conversation) {
        SQLiteDatabase db = getWritableDatabase();
        ContentValues row = new ContentValues();

        row.put("target_id", conversation.getTargetID());
        row.put("sender_id", conversation.getSenderID());
        row.put("target_name", conversation.getTargetName());
        row.put("target_photo", conversation.getTargetPhoto());
        row.put("status", conversation.getStatus());
        row.put("unread_count", conversation.getUnreadCount());
        row.put("last_message", conversation.getLastMessage());

        conversation.setConversationID(db.insert(TBL_CONVERSATIONS, null, row));
        Log.d(TAG, "conversation added: "+conversation.getConversationID());

        db.close();

        return conversation;
    }

The curious thing here is when I retrieve the insert id from insert method it returns the correct value, but the actual database field is null.