You know the answer of course…
but also: why aren’t you eating with your hosts or with friends?
If you are struggling with the food, a little honesty with your host family will go a long way. You can tell them that you appreciate the food, but it is very different than what you are used to. Figure out what you do like and ask for those foods. Ask if you can make them food sometimes- or use the kitchen to cook some food for yourself. Nobody can help if you don’t tell them what you need!
Also do actually make plans to eat with other English speakers. Use it for language practice or language break: today we will only speak (English/Japanese) during this meal. Try experimenting with food-as a group try a bunch of random unfamiliar but not too strange sounding dishes , and see who likes what this meal. Or, we will try all the Japanese ‘fast food’ chains (like Lotteria, noodle bowl places like Yoshinoya/ Matsuya, burger places like Freshness, etc). When you need a break, hit McDonalds.
Make a schedule of the places you want to visit before your mother comes, so that you know which ones to take her to: you want to know where they are, how to get there, what’s cool about it, etc. Block each one into your calendar specifically - Tuesday X, Thursday Y, Saturday, Z. Having a place you are scheduled to go and something you are scheduled to do makes a difference. For real. Pro level is asking somebody- foreigner or Japanese- to go with you!
You might have to (metaphorically) pick yourself up by the scruff of the neck and make yourself reach out to people to do these things. But it will help. Trying to will yourself into a different mindset is 10x harder than physically getting up and doing something different, something that puts you in charge of the situation.