My 3 yr old Yorkie, Sadie, has been acting peculiar for the last week or so. Actually, she developed a rash a few of weeks ago, I assume because I forgot to take her special "sensitive skin" shampoo along with her to the groomer's

In any case, this rash spread all up her spine, and I took her to the vet who said that the rash had become infected and gave her antibiotics. 90% of the rash cleared up within a few days, although a few bumps are still there. Not sure if this is at all related to our current problem, but thought I'd mention it.
So for the last week or so, she's had what I can only describe as a sick stomach. Last week she began acting very frantic (very similar to the time she swallowed a tin foil candy wrapper ... ugh!); she was eating a lot of grass, not vomitting though, and doing strange things like licking the floor or the baseboards in the kitchen. She licked my clothing, and tried to eat every plant in the house (which she's never done). Her stomach was making loud noises, so I took her to the vet again. The vet checked her over (no xray though) and said that since she was still eating, pooping and drinking to just keep an eye on her. She prescibed some Sulcrate for an upset stomach (every 12 hours) and also extended her antibiotics because she said that there were still a few spots that hadn't healed yet. After a day of the sulcrate, she seemed better ... until this morning. She's eating grass again, and acting quite unsettled. Her stomach is also making those rumbling sounds again. I gave her a dose of the Sulcrate and then (per instructions) gave her the antibiotic an hour later with food. Sadie only gets soft food a few times per week, so this is a real treat for her ... but she only sniffed it and walked away!! She did go back and eat it later (she'd had nothing else to eat that day), and she also did have a poop this morning ... I just can't think what could be wrong!!
She IS going into heat very soon - the signs and smells! - are obvious, and I"m wondering if anyone else has had ltheir yorkie have "upset stomach" symptoms when they are about to go into heat? The only other thing that I can think of is that I was giving her the antibiotic in a small bit of cream cheese (about the size of a pea), but have switched to giving it to her with about the same amount of peanut butter. When I tried to give her the pill this morning, she refused to take it with all of the "people food" she'd normally beg for: cream cheese, bread, etc., but finally did take it with peanut butter.
I'm really at a loss here and need your help!! The vet bills are getting expensive and my husband is not happy. I don't know if I should take her in again or wait it out some more. We're supposed to be going on a cruise at the end of April, and a friend of our family is staying here at the house with Sadie, but I don't want her to have to deal with a sick dog (or leave a sick dog at home without her mama, for that matter!!).
Advice or words of wisdom please!!
Wendy-Lee