If you run your P&L report and notice that it's missing budget data, first make sure that the budget record is specified as Reporting Budget.
Then, before you run the P&L report, click Customize and examine the Calendar parameter. The budget P&L is based on the budget setup. If the budget is fiscal, then the report should be ran on a Fiscal Calendar, and if the budget is operational, the report should be ran on an Operational Calendar.
For more information on budgets, see the Budgeting training articles. For more information on the P&L report, see the Profit and Loss training article.