u/Disastrous-Bus-7938

Hi everyone, im kinda struggling and i need advice/tips
ive been going to the gym for about a month and a half consistently now (every other day for about an hour and a half) increasing bicep curls from 10 pounds to 20 was easy but it feels like i have been trying to get to 30 forever now (about a week and a half)
20 pounds is super easy for me to go to 20 reps but as soon as i try to lift 30 i cant get more than 2 or 3 (my small gym doesnt have 25 pounds so i cant do that sadly)
am i doing something wrong or just not getting as strong as i thought? any advice is helpful, thank you