I recently had a urinalysis and urine culture, the one was fine, negative for everything. but the culture showed 10,000 - 20,000 to pseudomonas. is this an infection needing antibiotics?

Context is needed, such as symptoms or not, comorbidities and previous similar tests. The limit for number of colonies is 100000 in order to consider treating an infection. Asymptomatic bacteriuria or colonization is likely in your case.

Depends. If you had a normal urinalysis and are asymptomatic than the culture could be due to contamination. Wait a bit and then have it repeated taking care the specimen does not get contaminated. On these findings you don't need antibiotics. But if you have any symptoms see your urologist.