Mutual funds one time investment with different amount each month

Hi, I'm trying to start investing in mutual funds. The thing is, I don't have a stable expense pattern and income on a monthly basis, I'm a daily wager. So, can I invest in mutual funds using the one-time investment option with different amounts each month, like 1000 for one month and 3000 for the next? Will this have any issues in the long run, as I'm planning for long term investment? Also, will I have any difficulties when I try to withdraw the funds? Will this have any negative effect on my investment and profits? Kindly help me regarding this.