Please bare with me...I'll try to be as concise as I can.
Just hit the 6 month mark with my GF a few days ago.
Things had been going really well. Over Memorial day we went out of town to a nearby casino and stayed there for a couple nights and during that stretch of time we saw each other for 7 days straight and had sex each day. Had a blast.
This past weekend we had plans to hang out on Saturday, however she informed me the day before on Friday that she would have to work (she works a LOT - one of her jobs is part time at a restaurant a few times a week. I made a separate post about this). So we made tentative plans to hang out Saturday after she got off work. Well she didn't wind up getting off until 11PM and works about 35-40 minutes away from me so I told her that it probably wasn't gonna work that night (I had gone golfing earlier in the day and had met up with a buddy to watch the Stanley Cup). So by the time I had gotten home I was exhausted.
She was fine with this and the next morning (this past Sunday) texted me and apologized, saying how she was sorry it didn't work out the night before and for her schedule being so unpredictable.
She began housesitting for a friend of a friend yesterday, and will be there until Friday. Yesterday I drove over there with her and helped bring her bags in and made dinner and watched some TV. Also at this time I paid her what I thought to be $120 of the money that I owed for the casino trip over Memorial day weekend. Turns out I only gave her $100. An honest mistake.
Yesterday when I left her house she seemed fine (she was sick, has a ear/throat thing) so we didn't have sex. Plus she's house sitting so I dunno if that made sex more unlikely or not but anyway we didn't have any.
Today I don't hear from her at all, not until about 8PM or so. I texted her once around 11am saying "hi

you alive?". And then again at about 6PM saying "babe? you ok?". We normally text lots throughout the day so when I didn't hear from her at all until a couple hours ago, something seemed up.
And when she did reply, all she said was "Hey. I'm alive, just a busy day. Btw you shorted me money." So I'm thinking...OK...gee...nice to hear from you. I'm doing good, thanks for asking (sarcasm). So I playfully respond back "Dang it, you caught me

I must have only gave ya $100?" To which she replied "Yup". Normally she is much more talkative and playful etc.
At 10:30 when I was on my way home I texted her and said "awake?" and got no response, but she did read the text b/c of Iphone read receipt. So I tried calling her just to say hi, no answer.
I just have a bad feeling that something is up. I've been wracking my brain to think if I did or said something wrong and I can't think of anything. The only thing I can think of is shorting her $20 of the casino money I owed her which was an honest mistake, and I'll pay her the remaining $20 if I see her again, which to be honest I am having my doubts on. We haven't had sex since last Wednesday. We're supposed to hang out tomorrow but I doubt that will happen.
Throughout the course of the evening I've been preparing my head and heart for the worst and am to a spot where I'm almost expecting it. I do feel better than I did a few hours ago though.
Sorry for the huge novel. Does anything seem weird about this? Am I reading too much into it or is there legitimate cause for concern?
Any advice much appreciated.