I've lived in Tokyo 4 years and have some recommendations. I don't know how limited you are when you are 5 months pregnant........ but here are the recommendations anyway.
If you like Temples and breath taking scenary, try to make it Kyoto. I've never been, but people tell me it is fantastic. If you don't think you will ever come back to Japan, make sure to see Kyoto. I know I mentioned I haven't been, but I can say with 100 certainty that I will go before I leave Japan.
On Sunday.....goto Harajuku. There is a small street there that you can't miss. All the latest teen fashions, after hitting that street, walk over the bridge where there is all kinds of kids doing cos-play, and make your way to either the Temple (Meiji Jingu Mai) if you aren't tired of temples. Then make your way over to Yoyogi park and stroll around. You don't need to go into the park too far, maybe up to the small pond. THen go left and make you way to the street. Walk back to the station. Along this street there are many many many local Japanese bands playing.
The above recommendation is my favorite part of Tokyo.
After that, Shibulya is neat for again, more fashion, shopping, and people watching. Get a drink on the second floor Starbucks over looking the crazy crossway, and people watch. Walk around a little behind the Starbucks and check out the shops.
The Imperial Palace is somewhat amazing...... do this on a day when you are tired of seeing people.
shiji fish market. You have to go really early in the morning. Check out the tuna auction if you can. Only if seeing a massive fish market where sushi comes from interests you.
If you have a guide, check out a smaller old school area of Tokyo, west of Shinjuku is good for that. Koenji, Ogikabu, Nishi Ogikabu are three I recommend. So is Shimokitazawa.
Online look fot the metropolis Tokyo Magazine. There may be an band or famous singer in town you might want to see. If you like art gallerys Tokyo has tons. I think there is a huge Picasso showing going on then.