Can you give a bit more information about what your current diet is like? What's a typical day like for you?
As others have said, it might be worth having a chat with your GP and seeing if they can offer you some advice to stop the weight gain and get your onto a healthy eating path - whether that's just through dietary advice, referrals to an exercise scheme or someone more specialised, or if you need it, some help to work out what's going on for you.
It's worth having a look at
this to work out what your current BMR is. From that you can get a rough guideline on how many calories you need to maintain your current weight, and the common recommendation is to take around 500kcal off that in order to lose weight.
Personally I would really, really not recommend using shakes as a meal replacement. They're not a good strategy in the long-term (especially since many people use them as a 'quick fix', but then return back to eating in the old way so regain that weight), and in general you can make lunches which are far healthier and more nutritious and will still allow you to lose weight.
A healthy lunch could include e.g. a wholegrain pitta/wrap/sandwich with something like chicken, salad, peppers, whatever you like in it, or maybe soup and salad with a bread roll. A good basic starting guideline is a third/a third/a third (one third carbohydrate, one third protein/fat portion, one third fruits/vegetables), although it is just a basic guideline. You could prepare some salads in advance with things like salmon, avocado, rhubarb, seeds, peppers, all sorts. Anything like that is likely to satisfy you far more than shakes are (without meaning to sound patronising).