If I have a fixed rate mortgage then why is my house payment going up?

If you look at your statement you will probably find that the actual payment has gone down but that your taxes have gone up and so to have enough money in your escrow account to pay your taxes the amount that you pay to the mortgage company will be more. I know I was surprised when this happened to me also. If it helps at one point for a year it went down. I add an extra 50 dollars a month to pay my principal down and it has taken 15 years of payments off my mortgage.
Instead of 30 years I will own my condo in just 4 more years. You have to make sure that whatever you add extra is going toward the principal but what a difference this made.

If you did not put down 20%, then you probably have your taxes and insurance escrowed. If the escrow is short to pay these bills, they raise your payment to cover it.

If you escrow:

Your escrow minimum balance is not enough so they have raised the amount paid into escrow each month.

Your taxes went up

Your insurance went up

The projections for last years taxes/insurance were not enough so your escrow amount has been raised.

You can call your mortgage company and they will tell you why the payment went up.

Slow your paranoia down. Have you even asked the lender? They are adjusting your escrow account payment which covers both insurance and property tax. Adjustments after the first year are common as the escrow payment is necessarily estimated at the time the loan is funded.

Your payment will most likely go up every year, because property taxes and homeowners insurance go up every year.

Welcome to the joys of home ownership