Assigning instances based on Primary key in SQL

Question

My current data looks like this

OrderID | Category
1       | A 
1       | A 
1       | B 
1       | B 
1       | D 
2       | B 
3       | B 
3       | B 
3       | B 

What I would like is a kind of pivot, which shows a count of how many times an OrderID is placed in a particular category. The exception is for category 'B'. Every time an OrderID belongs to category B, I would like to display it as an instance of B_x where x is the xth instance of B being called. Therefore OrderID 1 would have B_1 and B_2, OrderID 2 would have just B_1, OrderID 3 would have B_1, B_2 and B_3. Therefore, the final results would be similar to this

OrderID | A | B_1 | B_2 | B_3 | D 
1       | 2 | 1   | 1   | 0   | 1 
2       | 0 | 1   | 0   | 0   | 0 
3       | 0 | 1   | 1   | 1   | 0 

I'm using SQL for this, so any pointers would be greatly appreciated!