Question: How do I know that I have a calling for the priesthood or monasticism?
Answer: Keep looking, and you will find it; keep knocking, and the door will open. It seems like you are not one hundred per cent sure, but the Lord will reveal that to you eventually. How do most people arrive? People are attached to this world by myriads of desires and short-lived pleasures - only to realise someday that none of these attachments gives them a full life. Their desires go unmet. They want more but are also losing interest.
I remember how I met God and came to church. I was leading an exciting life hitch-hiking to different exciting places. I was enjoying my freedom, but already getting bored with it. I needed more to keep my soul happy - more than just going anywhere and doing anything I wanted. A transition happened in my life and I ceased to enjoy things that used to give me pleasure and the company I used to like spending time with. It is in this transition that God's grace touched my soul and a new life began.
But coming back to your situation, it is perhaps worth remembering that one cannot have the Kingdom of God simply by observing the rules. What is the best choice - monasticism, or priesthood? One cannot decide that by drawing lots.
Our life is a journey. You are exploring your thoughts, desires and motives. They grow and ebb. Have patience, and eventually, you will make the right decision. You need the wisdom to wait. The Lord will let you know the answer sooner or later.