Hola Luis! De la bienvenida y yo espero que tenga una estancia maravillosa.
I second the suggestions made earlier for Saigon Sandwich and Tu Lan as excellent vietnamese at really inexpensive prices. Ask them to hold the chiles and Cristy should be fine spice wise.
The American Grilled Cheese Kitchen at Brannan and 2nd is a fantastic new lunch/brunch place. Expect a line, though they burn through orders pretty quick. South Park is right next to it which is a great little bit of seriously old school San Francisco, I heard it was our first "high end" neighborhood, before they put in the streetcar lines to make the hilly neighborhoods accessible pre-automobile.
Close to American Grilled Cheese is a jamaican place Primo Patio, that serves stuff pretty mild, but tasty. If you go Wednesday early enough for lunch you can get their jerk pork, which is a masterpiece of a thing, that isn't (or at least, wasn't) on the menu. It's magic. They've been there for ~20 years and are awesome, have a sort of urban patio. 3rd, on townsend.
Farmer Brown is another thought, close to where you're staying, "farm-fresh soul food", southern american food done just about as well as i know in this town. http://www.farmerbrownsf.com/ with only one entree over $20 i think it's a steal.
To me, Lafitte is the most exciting new restaurant here i've been to for combining ambiance, really interesting food and philosophy about it, and value. http://lafittesf.com/manifesto.html It's on the waterfront just north of the ferry building.
Definitely recommend the ferry building; Boullette's Larder has great take-out (though now that i think about it, it's a lot of take out and reheat).
For indian, close to where you are staying, I'd suggest Naan 'n Curry, exercising caution with the spiciness of the dishes ordered.
Really old school san francisco, Tadich or House of Prime Rib. But maybe I'm being too san franciscan by avoiding the fisherman's wharf area like the plague.
Cheap quality chinese soups (housemade noodles) within walking distance from you: Hon's won-tun house, kearny at ... sacramento or clay, i think. http://chowhound.chow.com/topics/370873
I may be being self-serving by suggesting these but I'd be really curious what you thought about my favorite tacquerias - I doubt they're all that Mexican really, sort of a San Francisco take on inexpensive and I think really good/interesting hybrid cuisine. My favorites are Cancun (mission @ 18th; the one closer to where you're staying, market at 6th, isn't as good), Altena and Faralito in that order, but this is a contentious subject as we San Franciscans do love our Tacquerias. I recommend http://www.burritoeater.com/ to get the spectrum (though I disagree with a significant percent of their reviews). Grease factor - most of these mission tacquerias i *assume* cook with lard, so that is that. I think of one burrito as two meals.
shoot. there is a great chinese soup-dumpling (soup inside dumpling) i found not too long ago but i can't remember the details beyond "richmond district".
Crab - generally not inexpensive - I go to Swan Oyster Depot, polk at california. Old school san francisco family kind of place, generally a line, closed sundays. It's a little cramped but I just love the place.
Bar Crudo is a fantastic italian raw seafood-centric joint on divisadero but I don't know if raw seafood, their specialty, is at all cool with the pregnancy. Skool (www.skoolsf.com) is another seafood centric place that I think is doing a great job, less raw stuff, maybe a little edgier than Bar Crudo.
Mid priced: Coco500 (kinda modern-old school hybrid), Orson (experimental/modern), Absinthe (classic brasserie kind of joint with a gorgeous bar on several levels).
If you dont mind the cab ride / bit of a long walk to Potrero Hill, I think Chez Mama is an astounding tiny french-ish neighborhood place with a ton of character - but at peak times expect a wait. Like 4 tables and a dozen seats at the bar, it's just it's own experience.
Fancy/high end: my faves are Gary Danko and Chez Spencer. Also, Chez Spencer operates a to-go truck at folsom and 7th that brings I think pretty high end dining to street food prices.
Best; hope you have a wonderful time here!
Saigon Sandwich Shop
House of Prime Rib
Swan Oyster Depot
Primo Patio Cafe
South Park Cafe
The San Franciscan
The American Grilled Cheese Kitchen