As per discription it seems your lower left first molar tooth has got dental caries... due to which u can feel the hole in the tooth & also feeling pain in it. You will have to get the treatment done for this tooth. You might have to get restoration ( filling) done in your decayed tooth or if cavity is deep, you might have to get Root canal done in the tooth. For correct diagnosis you can get the x- ray done for this tooth.
Next Steps
Get the xray done for this tooth.
Health Tips
Don't apply any toothpick, pin or anything directly to the tooth. If possible avoid extreme hot stuff from that side.