Is there a way to work out how many calories you should be eating when lifting, like there is for losing weight? I've lost almost all the weight i wanted to lose (moobs and gut are gone

) and have been doing stronglifts but feel like i'll need to eat more to actually start progressing in strength now rather than using it to lose weight.
I'm 5'7", 71KG and was eating 1500cals for a few months, have upped it to 2000 over the past couple of weeks but that's probably not enough. I just don't want to over-do it and end up putting fat back on
Yes, although you'll put fat back on regardless since it's impossible for 100% of your surplus to be used for hypertrophy purposes. The key is the rate of weight gain - you can't force-feed gains so you have to find a sweet spot where you're assuredly in a surplus (which will tend to go up as training becomes more intensive, NEAT goes up, your bw increases etc) but not too much of one, and at the other end of the scale not doing a me and ending up at maint. cals or thereabouts because you're being too cautious.
A couple of different guidelines:
Lyle McDonald uses something like this where you have 'proper' training experience and a rough idea of the maximum amount of weight you ideally want to be gaining:
Year 1 20-25lbs (2lbs per month) / 9 – 11 kg (0.9kg per month)
Year 2 10-12lbs (1lbs per month) / 4.5 – 5.5 kg (0.45kg per month)
Year 3 5-6lbs (0.5lbs per month) / 2 – 2.7 kg (0.22kg per month)
Year 4 2-3lbs / 0.9 – 1.3 kg
Year 5+ 2-3 lbs / 0.9 – 1.3kg
Alan Aragon uses something like this:
Beginner 1-1.5% of lean body mass per month
Intermediate 0.5-1% of lean body mass per month
Advanced 0.25-0.5% of lean body mass per month
I'm around Edenbridge. So Tonbridge or East Grinders are probably the nearest big towns.
Ah you're about 18 miles south of me then, by car anyway. </3 Definitely in the garden of England compared to me!