I think my new job is screwing me

I recently got a new job to support my family and was told the base pay was $17.24 an hour I was super happy it was $2.00 more than my last job and I was going to be on overnight so I was also excited to get the shift differential I’ve been here over a month and finished training but when I looked at my paystub nothing changed pay wise, I contacted my manager and he said “what are you talking about your shift differential is already included in your base pay?” If that’s the case my true base pay is $14.65 an hour which is way less than I made at my last job. I would have never accepted this job knowing that was the case. has anyone heard of this before? I haven’t any job I’ve ever had never did this. I contacted hr and am waiting for a reply but I’m wondering if I should seek out a lawyer for this cause I was not aware this was the agreement even in my offer letter it states base pay and nothing about it including the shift differential. What should I do?

UPDATE: he is claiming that this is how they always do this and I knew ahead of time that this is what I was accepting which is not true at all. Not one time in the interview or hiring process was I told that they molded base pay and shift differential together before offering I thought I was accepting a job at $17 an hour before the differential and I’ve now discovered I’m making $14.99 an hour which is a fucking dollar less than my last job. I feel tricked and I’m not happy about it. All my docs state base pay base pay base pay not once does it say they are combined! I’m wondering if I should let my manager know that I would not have accepted this job if they had been honest about it up front. They have told me that I should know this by the letter that the letter states it clearly and it does not. Should I contact a lawyer? This isn’t right