Is my tenant subleasing to someone else?

If he is subleasing, you can evict him. You would not be entitled to any money he made off it. I suggest you find out what’s going on. Try knocking on the door without notice and see who answers. See if the mail in the mailbox is addressed to him or someone else (do not take or open it, just look at it). You may have to spend some time watching the place to see who comes in and out. Find out whose name is on the utility bills. Document everything. Take photos of anyone you see entering the house. Take photos of any mail addressed to anyone besides the tenant. Check to see whose car is in the driveway. You should always visit your property often enough to know who lives there. 

You can't sue over a suspicion.  Verify it.  If she IS subleasing or if anyone else is living there, then evict for the violation and charge any and all damages to your tenant.

Have you actually gone to the house and CHECKED? If no sublet is permitted, you have grounds for eviction. Depending on the length of time he's been subletting, the condition of the property and the length of time left on the lease, you may be able to collect rent, damages and repair costs. BUT YOU NEED TO GO CHECK. 

Your recourse is to evict the tenant for their breach of contract, but you have no good cause to demand any rent collected by the tenant, only what you originally contracted the tenant to pay each month.

No you are not entitled to any of that money. Your recorse is to do an inspection (which you should have been doing pariodically) to confirm he is subleasing and evict him for the lease violation if he is. 

You are entitled to periodically visit the property to carry out full inspections - so do so. 

Also; you're entirely within your rights to review the rent when it comes to renewing the lease. 

If he's subletting, you can't get anything from the rent he's getting; but you can evict him.

You give notice of inspection and go find out.  No, you are not entitled to the profit.

Give the required minimum notice in writing that you will be doing an inspection ( where I live it is 24hours notice) and once notice is given and you have kept a copy of it, you can go and inspect and that should inform you if your tenant is subletting to someone else or not..... if the tenant is as per your contract, you give the tenant  notice to leave for breach of contract and take the tenant to court if they fail to leave ( including failing to remove their subtenant)........ it is very unlikely there is any way you can profit from any additional income your tenant got, but you can alway pay and take legal advice about landlord/tenant laws and claiming money locally to you...fact is even if there is a law where you live to do this, all the court will do is make a judgement in your favour and that never means the court collect it or the tenant pays it

No, you aren't entitled to the "profit" they are earning because you don't keep their rent at market level.

What you are entitled to is:

1. determine if they are really subleasing or not

2. provide a fix or quit notice, if they are.

3. decide that maybe it's better if they sublease so you don't have to deal with finding a new tenant... increase the rent.