Rehearsal sessions have increased, so my schedule is packed tight.
Literal
Rehearsal [possessive-の] frequency increased [reason-から] work jam-packed [casual-だよ].
リハ is a casual abbreviation of リハーサル ('rehearsal'). キチキチ is a mimetic for something packed tight with no room to spare — here applied to a work schedule. The abbreviation + mimetic combination is very natural casual speech among performers and creatives.